diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3fcfa96..7c9205b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,36 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [1.3.0] - 2026-05-28
+
+### Added
+
+- **Campaigns** service covering six endpoints, reached via `lettr.campaigns()`:
+  - `list()` / `list(ListCampaignsParams)` — paginated list with optional `status` filter (`GET /campaigns`)
+  - `get(id)` — single campaign with rendered `htmlContent` (`GET /campaigns/{id}`)
+  - `listEvents(id)` / `listEvents(id, ListCampaignEventsParams)` — cursor-paginated engagement events (`GET /campaigns/{id}/events`)
+  - `send(id)` — dispatch a draft now (`POST /campaigns/{id}/send`)
+  - `schedule(id, ScheduleCampaignOptions)` — schedule or reschedule (`POST /campaigns/{id}/schedule`)
+  - `unschedule(id)` — cancel a scheduled send (`POST /campaigns/{id}/unschedule`)
+- `CampaignStatus` and `CampaignEventType` enums (with `getValue()` for query building), plus `CampaignView`, `CampaignStats`, `CampaignEvent`, and `CampaignPagination` models
+- Unit tests covering campaign Gson deserialization, enum round-tripping, query-param building, and argument validation
+
+### Changed
+
+- `HttpClient.post(String path, Type responseType)` — new no-body overload, used by `Campaigns.send` / `unschedule` instead of passing a dummy empty map
+- `HttpClient.encodePathSegment(String)` — percent-encodes path segments so callers can safely interpolate arbitrary identifiers; adopted by `Campaigns` (id-taking methods) and `Emails.get` / `getScheduled` / `cancelScheduled`
+- `USER_AGENT` now reads the SDK version from a generated `com/lettr/version.properties` resource (templated by Gradle from `gradle.properties`) instead of a hardcoded string — single source of truth across releases
+- `OffsetPagination` (`com.lettr.core.model`) — shared pagination shape for new code; `ListCampaignsResponse` uses it. `AudiencePagination` is unchanged and remains the return type of the audience list responses (both classes have identical shape)
+- `PageParams` (`com.lettr.core.model`) — shared listing parameters for new code; `ListCampaignsParams` composes it. `com.lettr.services.audience.model.PageParams` is unchanged and continues to work for existing audience usage (both classes are behaviourally identical)
+- `WireValues.of(Enum)` (`com.lettr.core.util`) reads `@SerializedName` reflectively for URL query building, so enums declare each wire value exactly once
+- `Args.requireNonEmpty(name, value)` / `Args.requireNonNull(name, value)` (`com.lettr.core.util`) — shared validators; adopted by `Campaigns` and `ScheduleCampaignOptions`
+- `getCampaigns()` / `getEvents()` (and the audience list responses) defensively return `Collections.emptyList()` when the API omits the list field, so `@Nonnull` getters never return null
+
+### Notes
+
+- `CampaignView.htmlContent` is only populated by `get(...)`; it is `null` on list, send, schedule, and unschedule responses
+- Campaign events use cursor pagination — keep requesting with `getNextCursor()` until it is `null`; a filtered page may return an empty `events` list with a non-null cursor, meaning more pages remain
+
 ## [1.2.0] - 2026-05-25
 
 ### Added
diff --git a/README.md b/README.md
index 45d90ae..b259471 100644
--- a/README.md
+++ b/README.md
@@ -7,7 +7,7 @@ The official Java SDK for the [Lettr](https://lettr.com) Email API. Send transac
 ### Gradle
 
 ```groovy
-implementation 'com.lettr:lettr-java:1.2.0'
+implementation 'com.lettr:lettr-java:1.3.0'
 ```
 
 ### Maven
@@ -16,7 +16,7 @@ implementation 'com.lettr:lettr-java:1.2.0'
 <dependency>
     <groupId>com.lettr</groupId>
     <artifactId>lettr-java</artifactId>
-    <version>1.2.0</version>
+    <version>1.3.0</version>
 </dependency>
 ```
 
@@ -425,6 +425,99 @@ System.out.println("Subject: " + html.getSubject());
 System.out.println("HTML: " + html.getHtml());
 ```
 
+## Campaigns
+
+### List Campaigns
+
+```java
+import com.lettr.services.campaigns.model.*;
+
+// List with default pagination
+ListCampaignsResponse campaigns = lettr.campaigns().list();
+
+// List with filters
+ListCampaignsResponse drafts = lettr.campaigns().list(
+    ListCampaignsParams.builder()
+        .status(CampaignStatus.DRAFT)
+        .perPage(50)
+        .build()
+);
+
+for (CampaignView c : drafts.getCampaigns()) {
+    System.out.println(c.getName() + " - " + c.getStatus() + " (sent: " + c.getSentCount() + ")");
+}
+System.out.println("Page " + drafts.getPagination().getCurrentPage()
+        + " of " + drafts.getPagination().getLastPage());
+```
+
+### Get a Campaign
+
+```java
+CampaignView campaign = lettr.campaigns().get("0193e6a8-1f3a-7c2a-b9e2-1aa1d2e5d3f0");
+
+System.out.println("Status: " + campaign.getStatus());
+System.out.println("HTML: " + campaign.getHtmlContent());   // only populated by get(...)
+
+CampaignStats stats = campaign.getStats();
+System.out.println("Opens: " + stats.getUniqueOpens() + " / Clicks: " + stats.getUniqueClicks());
+```
+
+### List Campaign Events
+
+Events use cursor-based pagination. Keep requesting with the returned cursor until
+it is `null`. A filtered page may come back with no events but a non-null cursor —
+that means more pages remain, so keep going.
+
+```java
+String cursor = null;
+do {
+    ListCampaignEventsResponse page = lettr.campaigns().listEvents(
+        campaign.getId(),
+        ListCampaignEventsParams.builder()
+            .eventType(CampaignEventType.CLICK)
+            .email("user@example.com")
+            .startDate("2026-05-01")
+            .limit(100)
+            .cursor(cursor)
+            .build()
+    );
+
+    for (CampaignEvent event : page.getEvents()) {
+        System.out.println(event.getEventType() + " at " + event.getTimestamp()
+                + " -> " + event.getTargetLinkUrl());
+    }
+
+    cursor = page.getNextCursor();
+} while (cursor != null);
+```
+
+### Send a Campaign
+
+```java
+// Immediately dispatches a draft; the campaign transitions to "preparing".
+CampaignView sending = lettr.campaigns().send(campaign.getId());
+System.out.println("Status: " + sending.getStatus());
+```
+
+### Schedule a Campaign
+
+```java
+// Schedule (or reschedule) for future delivery. Include a timezone offset.
+CampaignView scheduled = lettr.campaigns().schedule(
+    campaign.getId(),
+    ScheduleCampaignOptions.of("2026-06-01T09:00:00+00:00")
+);
+System.out.println("Scheduled for: " + scheduled.getScheduledAt());
+```
+
+### Unschedule a Campaign
+
+```java
+// Cancel a scheduled send, returning the campaign to "draft".
+CampaignView draft = lettr.campaigns().unschedule(campaign.getId());
+System.out.println("Status: " + draft.getStatus());
+```
+
 ## System
 
 ### Health Check
diff --git a/build.gradle b/build.gradle
index d69cb94..64492ec 100644
--- a/build.gradle
+++ b/build.gradle
@@ -30,6 +30,12 @@ test {
     useJUnitPlatform()
 }
 
+processResources {
+    filesMatching('com/lettr/version.properties') {
+        expand(version: project.version)
+    }
+}
+
 publishing {
     publications {
         mavenJava(MavenPublication) {
diff --git a/gradle.properties b/gradle.properties
index 4ec527c..403c4d6 100644
--- a/gradle.properties
+++ b/gradle.properties
@@ -1,5 +1,5 @@
 GROUP=com.lettr
-VERSION=1.2.0
+VERSION=1.3.0
 POM_ARTIFACT_ID=lettr-java
 POM_NAME=Lettr Java SDK
 POM_DESCRIPTION=Java SDK for the Lettr Email API
diff --git a/src/main/java/com/lettr/Lettr.java b/src/main/java/com/lettr/Lettr.java
index 225ba81..c518dae 100644
--- a/src/main/java/com/lettr/Lettr.java
+++ b/src/main/java/com/lettr/Lettr.java
@@ -1,6 +1,7 @@
 package com.lettr;
 
 import com.lettr.services.audience.Audience;
+import com.lettr.services.campaigns.Campaigns;
 import com.lettr.services.domains.Domains;
 import com.lettr.services.emails.Emails;
 import com.lettr.services.projects.Projects;
@@ -67,4 +68,7 @@ public Lettr(@Nonnull String apiKey) {
 
     /** Returns the Audience namespace for managing lists, contacts, topics, properties, and segments. */
     @Nonnull public Audience audience() { return new Audience(apiKey); }
+
+    /** Returns the Campaigns service for listing, sending, and scheduling campaigns. */
+    @Nonnull public Campaigns campaigns() { return new Campaigns(apiKey); }
 }
diff --git a/src/main/java/com/lettr/core/model/OffsetPagination.java b/src/main/java/com/lettr/core/model/OffsetPagination.java
new file mode 100644
index 0000000..4e01129
--- /dev/null
+++ b/src/main/java/com/lettr/core/model/OffsetPagination.java
@@ -0,0 +1,45 @@
+package com.lettr.core.model;
+
+import com.google.gson.annotations.SerializedName;
+
+/**
+ * Offset-based pagination metadata returned alongside paginated list responses
+ * across the SDK (audience, campaigns, …).
+ */
+public class OffsetPagination {
+
+    private int total;
+
+    @SerializedName("per_page")
+    private int perPage;
+
+    @SerializedName("current_page")
+    private int currentPage;
+
+    @SerializedName("last_page")
+    private int lastPage;
+
+    public int getTotal() {
+        return total;
+    }
+
+    public int getPerPage() {
+        return perPage;
+    }
+
+    public int getCurrentPage() {
+        return currentPage;
+    }
+
+    public int getLastPage() {
+        return lastPage;
+    }
+
+    @Override
+    public String toString() {
+        return "OffsetPagination{total=" + total
+                + ", perPage=" + perPage
+                + ", currentPage=" + currentPage
+                + ", lastPage=" + lastPage + '}';
+    }
+}
diff --git a/src/main/java/com/lettr/core/model/PageParams.java b/src/main/java/com/lettr/core/model/PageParams.java
new file mode 100644
index 0000000..f465d22
--- /dev/null
+++ b/src/main/java/com/lettr/core/model/PageParams.java
@@ -0,0 +1,71 @@
+package com.lettr.core.model;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+/**
+ * Shared {@code page} / {@code per_page} parameters used by every listing
+ * endpoint that supports offset-based pagination. Composable into service-specific
+ * param classes that add further filters (see e.g. {@code ListCampaignsParams}).
+ */
+public class PageParams {
+
+    private final Integer page;
+    private final Integer perPage;
+
+    private PageParams(Builder builder) {
+        this.page = builder.page;
+        this.perPage = builder.perPage;
+    }
+
+    @Nonnull
+    public static Builder builder() {
+        return new Builder();
+    }
+
+    @Nullable
+    public Integer getPage() {
+        return page;
+    }
+
+    @Nullable
+    public Integer getPerPage() {
+        return perPage;
+    }
+
+    @Nonnull
+    public Map<String, String> toQueryParams() {
+        Map<String, String> params = new LinkedHashMap<>();
+        if (page != null) params.put("page", page.toString());
+        if (perPage != null) params.put("per_page", perPage.toString());
+        return params;
+    }
+
+    public static class Builder {
+        private Integer page;
+        private Integer perPage;
+
+        private Builder() {}
+
+        /** <b>(optional)</b> Page number (min 1, default 1). */
+        @Nonnull
+        public Builder page(@Nullable Integer page) {
+            this.page = page;
+            return this;
+        }
+
+        /** <b>(optional)</b> Items per page (1–100, default 20). */
+        @Nonnull
+        public Builder perPage(@Nullable Integer perPage) {
+            this.perPage = perPage;
+            return this;
+        }
+
+        @Nonnull
+        public PageParams build() {
+            return new PageParams(this);
+        }
+    }
+}
diff --git a/src/main/java/com/lettr/core/net/HttpClient.java b/src/main/java/com/lettr/core/net/HttpClient.java
index 4350937..7ea1f45 100644
--- a/src/main/java/com/lettr/core/net/HttpClient.java
+++ b/src/main/java/com/lettr/core/net/HttpClient.java
@@ -11,6 +11,7 @@
 import com.lettr.core.exception.LettrValidationException;
 
 import java.io.IOException;
+import java.io.InputStream;
 import java.lang.reflect.Type;
 import java.net.URI;
 import java.net.http.HttpRequest;
@@ -20,6 +21,7 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Properties;
 
 /**
  * Internal HTTP client for communicating with the Lettr API.
@@ -27,7 +29,8 @@
 public class HttpClient {
 
     private static final String BASE_URL = "https://app.lettr.com/api";
-    private static final String USER_AGENT = "lettr-java/1.2.0";
+    private static final String SDK_VERSION = loadVersion();
+    private static final String USER_AGENT = "lettr-java/" + SDK_VERSION;
     private static final Duration DEFAULT_TIMEOUT = Duration.ofSeconds(30);
 
     private final String apiKey;
@@ -96,6 +99,32 @@ public <T> T post(String path, Object body, Type responseType) throws LettrExcep
         return execute(request, responseType);
     }
 
+    /**
+     * Perform a POST request with no body, returning a deserialized response.
+     * Used by endpoints whose only input is the path parameter (e.g.
+     * {@code /campaigns/{id}/send}).
+     *
+     * @param path         API path
+     * @param responseType the type to deserialize the "data" field into
+     * @param <T>          response data type
+     * @return deserialized response data
+     * @throws LettrException on error
+     */
+    public <T> T post(String path, Type responseType) throws LettrException {
+        String url = buildUrl(path, null);
+
+        HttpRequest request = HttpRequest.newBuilder()
+                .uri(URI.create(url))
+                .timeout(DEFAULT_TIMEOUT)
+                .header("Authorization", "Bearer " + apiKey)
+                .header("Accept", "application/json")
+                .header("User-Agent", USER_AGENT)
+                .POST(HttpRequest.BodyPublishers.noBody())
+                .build();
+
+        return execute(request, responseType);
+    }
+
     /**
      * Perform a PUT request with a JSON body.
      *
@@ -235,6 +264,23 @@ public <T> T delete(String path, Object body, Type responseType) throws LettrExc
         return execute(request, responseType);
     }
 
+    /**
+     * Percent-encode a single URL path segment so callers can safely interpolate
+     * arbitrary identifiers ({@code /campaigns/" + encodePathSegment(id)}).
+     * Encodes reserved characters including {@code /}, {@code ?}, {@code #},
+     * and spaces; produces RFC 3986-compatible output.
+     */
+    public static String encodePathSegment(String segment) {
+        if (segment == null) {
+            return "";
+        }
+        // URLEncoder is form-encoded ('+' for space, '*' un-encoded); fix to RFC 3986.
+        return java.net.URLEncoder.encode(segment, java.nio.charset.StandardCharsets.UTF_8)
+                .replace("+", "%20")
+                .replace("*", "%2A")
+                .replace("%7E", "~");
+    }
+
     private void executeNoResponse(HttpRequest request) throws LettrException {
         try {
             HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());
@@ -354,4 +400,22 @@ private String encodeParam(String value) {
     public Gson getGson() {
         return gson;
     }
+
+    private static String loadVersion() {
+        try (InputStream in = HttpClient.class.getResourceAsStream("/com/lettr/version.properties")) {
+            if (in == null) {
+                return "unknown";
+            }
+            Properties props = new Properties();
+            props.load(in);
+            String v = props.getProperty("version");
+            // Guard against unprocessed templates: "@version@", "${version}", or empty.
+            if (v == null || v.isEmpty() || v.startsWith("@") || v.contains("${")) {
+                return "unknown";
+            }
+            return v;
+        } catch (IOException e) {
+            return "unknown";
+        }
+    }
 }
diff --git a/src/main/java/com/lettr/core/util/Args.java b/src/main/java/com/lettr/core/util/Args.java
new file mode 100644
index 0000000..f8bf9e2
--- /dev/null
+++ b/src/main/java/com/lettr/core/util/Args.java
@@ -0,0 +1,40 @@
+package com.lettr.core.util;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
+/**
+ * Argument validation helpers used at SDK entry points to reject obviously
+ * invalid input early, with a consistent {@code "<name> is required"} message.
+ */
+public final class Args {
+
+    private Args() {}
+
+    /**
+     * Throws {@link IllegalArgumentException} if {@code value} is {@code null}
+     * or empty.
+     *
+     * @param name  the parameter name, used in the exception message
+     * @param value the value to check
+     * @return {@code value} unchanged, so this can be used as an expression
+     */
+    @Nonnull
+    public static String requireNonEmpty(@Nonnull String name, @Nullable String value) {
+        if (value == null || value.isEmpty()) {
+            throw new IllegalArgumentException(name + " is required");
+        }
+        return value;
+    }
+
+    /**
+     * Throws {@link IllegalArgumentException} if {@code value} is {@code null}.
+     */
+    @Nonnull
+    public static <T> T requireNonNull(@Nonnull String name, @Nullable T value) {
+        if (value == null) {
+            throw new IllegalArgumentException(name + " is required");
+        }
+        return value;
+    }
+}
diff --git a/src/main/java/com/lettr/core/util/WireValues.java b/src/main/java/com/lettr/core/util/WireValues.java
new file mode 100644
index 0000000..e5f2078
--- /dev/null
+++ b/src/main/java/com/lettr/core/util/WireValues.java
@@ -0,0 +1,37 @@
+package com.lettr.core.util;
+
+import com.google.gson.annotations.SerializedName;
+
+import javax.annotation.Nonnull;
+import java.lang.reflect.Field;
+
+/**
+ * Reads the {@link SerializedName} value of an enum constant for use in URL
+ * query parameters. Lets enum classes declare each wire value exactly once
+ * (on {@code @SerializedName}) instead of duplicating it in a {@code value}
+ * field for query building.
+ */
+public final class WireValues {
+
+    private WireValues() {}
+
+    /**
+     * Returns the {@code @SerializedName} value of the given enum constant,
+     * matching how Gson serializes/deserializes it. Falls back to {@link Enum#name()}
+     * if the constant has no {@code @SerializedName} annotation.
+     */
+    @Nonnull
+    public static String of(@Nonnull Enum<?> value) {
+        if (value == null) {
+            throw new IllegalArgumentException("enum value is required");
+        }
+        try {
+            Field field = value.getDeclaringClass().getField(value.name());
+            SerializedName annotation = field.getAnnotation(SerializedName.class);
+            return annotation != null ? annotation.value() : value.name();
+        } catch (NoSuchFieldException e) {
+            // Should be unreachable: Enum#name() always corresponds to a declared field.
+            return value.name();
+        }
+    }
+}
diff --git a/src/main/java/com/lettr/services/audience/contacts/model/ListAudienceContactsResponse.java b/src/main/java/com/lettr/services/audience/contacts/model/ListAudienceContactsResponse.java
index d0bb5ea..9551454 100644
--- a/src/main/java/com/lettr/services/audience/contacts/model/ListAudienceContactsResponse.java
+++ b/src/main/java/com/lettr/services/audience/contacts/model/ListAudienceContactsResponse.java
@@ -3,6 +3,7 @@
 import com.lettr.services.audience.model.AudiencePagination;
 
 import javax.annotation.Nonnull;
+import java.util.Collections;
 import java.util.List;
 
 public class ListAudienceContactsResponse {
@@ -12,7 +13,7 @@ public class ListAudienceContactsResponse {
 
     @Nonnull
     public List<AudienceContactView> getContacts() {
-        return contacts;
+        return contacts != null ? contacts : Collections.emptyList();
     }
 
     @Nonnull
diff --git a/src/main/java/com/lettr/services/audience/lists/model/ListAudienceListsResponse.java b/src/main/java/com/lettr/services/audience/lists/model/ListAudienceListsResponse.java
index bcb7f19..e77ef31 100644
--- a/src/main/java/com/lettr/services/audience/lists/model/ListAudienceListsResponse.java
+++ b/src/main/java/com/lettr/services/audience/lists/model/ListAudienceListsResponse.java
@@ -3,6 +3,7 @@
 import com.lettr.services.audience.model.AudiencePagination;
 
 import javax.annotation.Nonnull;
+import java.util.Collections;
 import java.util.List;
 
 public class ListAudienceListsResponse {
@@ -12,7 +13,7 @@ public class ListAudienceListsResponse {
 
     @Nonnull
     public List<AudienceListView> getLists() {
-        return lists;
+        return lists != null ? lists : Collections.emptyList();
     }
 
     @Nonnull
diff --git a/src/main/java/com/lettr/services/audience/model/AudiencePagination.java b/src/main/java/com/lettr/services/audience/model/AudiencePagination.java
index cdd4384..c9d451a 100644
--- a/src/main/java/com/lettr/services/audience/model/AudiencePagination.java
+++ b/src/main/java/com/lettr/services/audience/model/AudiencePagination.java
@@ -4,6 +4,10 @@
 
 /**
  * Pagination metadata returned alongside paginated audience list responses.
+ *
+ * <p>Identical in shape to {@link com.lettr.core.model.OffsetPagination}; both
+ * are supported. New code may prefer the core type; existing imports of this
+ * class continue to work unchanged.</p>
  */
 public class AudiencePagination {
 
diff --git a/src/main/java/com/lettr/services/audience/model/PageParams.java b/src/main/java/com/lettr/services/audience/model/PageParams.java
index 3d521d5..c030552 100644
--- a/src/main/java/com/lettr/services/audience/model/PageParams.java
+++ b/src/main/java/com/lettr/services/audience/model/PageParams.java
@@ -6,8 +6,11 @@
 import java.util.Map;
 
 /**
- * Shared page/per_page parameters used by listing endpoints that only
- * support pagination (no other filters).
+ * Shared page/per_page parameters used by the audience listing endpoints.
+ *
+ * <p>Identical in behaviour to {@link com.lettr.core.model.PageParams}; both are
+ * supported. New code may prefer the core type; existing imports of this class
+ * continue to work unchanged.</p>
  */
 public class PageParams {
 
diff --git a/src/main/java/com/lettr/services/audience/properties/model/ListAudiencePropertiesResponse.java b/src/main/java/com/lettr/services/audience/properties/model/ListAudiencePropertiesResponse.java
index 3308f3c..0b190fc 100644
--- a/src/main/java/com/lettr/services/audience/properties/model/ListAudiencePropertiesResponse.java
+++ b/src/main/java/com/lettr/services/audience/properties/model/ListAudiencePropertiesResponse.java
@@ -3,6 +3,7 @@
 import com.lettr.services.audience.model.AudiencePagination;
 
 import javax.annotation.Nonnull;
+import java.util.Collections;
 import java.util.List;
 
 public class ListAudiencePropertiesResponse {
@@ -10,7 +11,7 @@ public class ListAudiencePropertiesResponse {
     private List<AudiencePropertyView> properties;
     private AudiencePagination pagination;
 
-    @Nonnull public List<AudiencePropertyView> getProperties() { return properties; }
+    @Nonnull public List<AudiencePropertyView> getProperties() { return properties != null ? properties : Collections.emptyList(); }
     @Nonnull public AudiencePagination getPagination() { return pagination; }
 
     @Override
diff --git a/src/main/java/com/lettr/services/audience/segments/model/ListAudienceSegmentsResponse.java b/src/main/java/com/lettr/services/audience/segments/model/ListAudienceSegmentsResponse.java
index bec03ce..442ee8d 100644
--- a/src/main/java/com/lettr/services/audience/segments/model/ListAudienceSegmentsResponse.java
+++ b/src/main/java/com/lettr/services/audience/segments/model/ListAudienceSegmentsResponse.java
@@ -3,6 +3,7 @@
 import com.lettr.services.audience.model.AudiencePagination;
 
 import javax.annotation.Nonnull;
+import java.util.Collections;
 import java.util.List;
 
 public class ListAudienceSegmentsResponse {
@@ -10,7 +11,7 @@ public class ListAudienceSegmentsResponse {
     private List<AudienceSegmentView> segments;
     private AudiencePagination pagination;
 
-    @Nonnull public List<AudienceSegmentView> getSegments() { return segments; }
+    @Nonnull public List<AudienceSegmentView> getSegments() { return segments != null ? segments : Collections.emptyList(); }
     @Nonnull public AudiencePagination getPagination() { return pagination; }
 
     @Override
diff --git a/src/main/java/com/lettr/services/audience/topics/model/ListAudienceTopicsResponse.java b/src/main/java/com/lettr/services/audience/topics/model/ListAudienceTopicsResponse.java
index 364cb80..1683716 100644
--- a/src/main/java/com/lettr/services/audience/topics/model/ListAudienceTopicsResponse.java
+++ b/src/main/java/com/lettr/services/audience/topics/model/ListAudienceTopicsResponse.java
@@ -3,6 +3,7 @@
 import com.lettr.services.audience.model.AudiencePagination;
 
 import javax.annotation.Nonnull;
+import java.util.Collections;
 import java.util.List;
 
 public class ListAudienceTopicsResponse {
@@ -10,7 +11,7 @@ public class ListAudienceTopicsResponse {
     private List<AudienceTopicView> topics;
     private AudiencePagination pagination;
 
-    @Nonnull public List<AudienceTopicView> getTopics() { return topics; }
+    @Nonnull public List<AudienceTopicView> getTopics() { return topics != null ? topics : Collections.emptyList(); }
     @Nonnull public AudiencePagination getPagination() { return pagination; }
 
     @Override
diff --git a/src/main/java/com/lettr/services/campaigns/Campaigns.java b/src/main/java/com/lettr/services/campaigns/Campaigns.java
new file mode 100644
index 0000000..029b884
--- /dev/null
+++ b/src/main/java/com/lettr/services/campaigns/Campaigns.java
@@ -0,0 +1,125 @@
+package com.lettr.services.campaigns;
+
+import com.lettr.core.exception.LettrException;
+import com.lettr.core.net.HttpClient;
+import com.lettr.core.util.Args;
+import com.lettr.services.BaseService;
+import com.lettr.services.campaigns.model.*;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
+/**
+ * Service for listing, inspecting, sending, and scheduling campaigns via the
+ * Lettr API. Read operations require the {@code campaigns:read} scope; send,
+ * schedule, and unschedule require {@code campaigns:write} and are not available
+ * to sandbox keys.
+ */
+public class Campaigns extends BaseService {
+
+    public Campaigns(@Nonnull String apiKey) {
+        super(apiKey);
+    }
+
+    /**
+     * List campaigns with optional filtering and pagination.
+     *
+     * @param params optional query parameters; pass null for defaults
+     * @return a page of campaigns with pagination metadata
+     * @throws LettrException if the request fails
+     */
+    @Nonnull
+    public ListCampaignsResponse list(@Nullable ListCampaignsParams params) throws LettrException {
+        return httpClient.get("/campaigns", params != null ? params.toQueryParams() : null, ListCampaignsResponse.class);
+    }
+
+    /** List campaigns with default pagination. */
+    @Nonnull
+    public ListCampaignsResponse list() throws LettrException {
+        return list(null);
+    }
+
+    /**
+     * Retrieve a single campaign, including its rendered HTML content.
+     *
+     * @param campaignId the campaign ID
+     * @return the campaign
+     * @throws LettrException if the request fails
+     * @throws IllegalArgumentException if {@code campaignId} is null or empty
+     */
+    @Nonnull
+    public CampaignView get(@Nonnull String campaignId) throws LettrException {
+        Args.requireNonEmpty("campaignId", campaignId);
+        return httpClient.get("/campaigns/" + HttpClient.encodePathSegment(campaignId), null, CampaignView.class);
+    }
+
+    /**
+     * List engagement events for a campaign with optional filtering. Uses
+     * cursor-based pagination via {@link ListCampaignEventsResponse#getNextCursor()}.
+     *
+     * @param campaignId the campaign ID
+     * @param params     optional query parameters; pass null for defaults
+     * @return a page of events with a next-page cursor
+     * @throws LettrException if the request fails
+     * @throws IllegalArgumentException if {@code campaignId} is null or empty
+     */
+    @Nonnull
+    public ListCampaignEventsResponse listEvents(@Nonnull String campaignId, @Nullable ListCampaignEventsParams params) throws LettrException {
+        Args.requireNonEmpty("campaignId", campaignId);
+        return httpClient.get("/campaigns/" + HttpClient.encodePathSegment(campaignId) + "/events",
+                params != null ? params.toQueryParams() : null,
+                ListCampaignEventsResponse.class);
+    }
+
+    /** List campaign engagement events with default parameters. */
+    @Nonnull
+    public ListCampaignEventsResponse listEvents(@Nonnull String campaignId) throws LettrException {
+        return listEvents(campaignId, null);
+    }
+
+    /**
+     * Immediately send a draft campaign. Sending is asynchronous; the campaign
+     * transitions to {@code preparing}.
+     *
+     * @param campaignId the campaign ID
+     * @return the updated campaign
+     * @throws LettrException if the request fails
+     * @throws IllegalArgumentException if {@code campaignId} is null or empty
+     */
+    @Nonnull
+    public CampaignView send(@Nonnull String campaignId) throws LettrException {
+        Args.requireNonEmpty("campaignId", campaignId);
+        return httpClient.post("/campaigns/" + HttpClient.encodePathSegment(campaignId) + "/send", CampaignView.class);
+    }
+
+    /**
+     * Schedule a campaign for future delivery, or reschedule an already-scheduled
+     * campaign to a new time.
+     *
+     * @param campaignId the campaign ID
+     * @param options    schedule options including {@code scheduledAt}
+     * @return the updated campaign
+     * @throws LettrException if the request fails
+     * @throws IllegalArgumentException if {@code campaignId} is null/empty or {@code options} is null
+     */
+    @Nonnull
+    public CampaignView schedule(@Nonnull String campaignId, @Nonnull ScheduleCampaignOptions options) throws LettrException {
+        Args.requireNonEmpty("campaignId", campaignId);
+        Args.requireNonNull("options", options);
+        return httpClient.post("/campaigns/" + HttpClient.encodePathSegment(campaignId) + "/schedule", options, CampaignView.class);
+    }
+
+    /**
+     * Cancel a scheduled send, returning the campaign to {@code draft}.
+     *
+     * @param campaignId the campaign ID
+     * @return the updated campaign
+     * @throws LettrException if the request fails
+     * @throws IllegalArgumentException if {@code campaignId} is null or empty
+     */
+    @Nonnull
+    public CampaignView unschedule(@Nonnull String campaignId) throws LettrException {
+        Args.requireNonEmpty("campaignId", campaignId);
+        return httpClient.post("/campaigns/" + HttpClient.encodePathSegment(campaignId) + "/unschedule", CampaignView.class);
+    }
+}
diff --git a/src/main/java/com/lettr/services/campaigns/model/CampaignEvent.java b/src/main/java/com/lettr/services/campaigns/model/CampaignEvent.java
new file mode 100644
index 0000000..6b4326f
--- /dev/null
+++ b/src/main/java/com/lettr/services/campaigns/model/CampaignEvent.java
@@ -0,0 +1,82 @@
+package com.lettr.services.campaigns.model;
+
+import com.google.gson.annotations.SerializedName;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
+/**
+ * A single campaign engagement event (open, click, bounce, etc.).
+ */
+public class CampaignEvent {
+
+    @SerializedName("event_id")
+    private String eventId;
+
+    @SerializedName("event_type")
+    private CampaignEventType eventType;
+
+    private String email;
+    private String timestamp;
+
+    @SerializedName("bounce_class")
+    private String bounceClass;
+
+    private String reason;
+
+    @SerializedName("target_link_url")
+    private String targetLinkUrl;
+
+    @SerializedName("user_agent")
+    private String userAgent;
+
+    @Nonnull
+    public String getEventId() {
+        return eventId;
+    }
+
+    @Nonnull
+    public CampaignEventType getEventType() {
+        return eventType;
+    }
+
+    @Nonnull
+    public String getEmail() {
+        return email;
+    }
+
+    @Nonnull
+    public String getTimestamp() {
+        return timestamp;
+    }
+
+    /** SparkPost bounce classification code; only set on bounce events. */
+    @Nullable
+    public String getBounceClass() {
+        return bounceClass;
+    }
+
+    /** Failure or bounce reason, if any. */
+    @Nullable
+    public String getReason() {
+        return reason;
+    }
+
+    /** Clicked link URL; only set on click events. */
+    @Nullable
+    public String getTargetLinkUrl() {
+        return targetLinkUrl;
+    }
+
+    /** Recipient user agent; only set on open/click events. */
+    @Nullable
+    public String getUserAgent() {
+        return userAgent;
+    }
+
+    @Override
+    public String toString() {
+        return "CampaignEvent{eventId='" + eventId + "', eventType=" + eventType
+                + ", email='" + email + "', timestamp='" + timestamp + "'}";
+    }
+}
diff --git a/src/main/java/com/lettr/services/campaigns/model/CampaignEventType.java b/src/main/java/com/lettr/services/campaigns/model/CampaignEventType.java
new file mode 100644
index 0000000..cd80312
--- /dev/null
+++ b/src/main/java/com/lettr/services/campaigns/model/CampaignEventType.java
@@ -0,0 +1,17 @@
+package com.lettr.services.campaigns.model;
+
+import com.google.gson.annotations.SerializedName;
+
+/**
+ * Type of campaign engagement event. Wire values are defined by {@code @SerializedName};
+ * use {@link com.lettr.core.util.WireValues#of(Enum)} to retrieve them.
+ */
+public enum CampaignEventType {
+    @SerializedName("injection") INJECTION,
+    @SerializedName("delivery") DELIVERY,
+    @SerializedName("bounce") BOUNCE,
+    @SerializedName("spam_complaint") SPAM_COMPLAINT,
+    @SerializedName("open") OPEN,
+    @SerializedName("click") CLICK,
+    @SerializedName("list_unsubscribe") LIST_UNSUBSCRIBE
+}
diff --git a/src/main/java/com/lettr/services/campaigns/model/CampaignStats.java b/src/main/java/com/lettr/services/campaigns/model/CampaignStats.java
new file mode 100644
index 0000000..c9c39b1
--- /dev/null
+++ b/src/main/java/com/lettr/services/campaigns/model/CampaignStats.java
@@ -0,0 +1,77 @@
+package com.lettr.services.campaigns.model;
+
+import com.google.gson.annotations.SerializedName;
+
+/**
+ * Aggregated engagement statistics embedded in every campaign response.
+ */
+public class CampaignStats {
+
+    private int injections;
+    private int deliveries;
+    private int bounces;
+
+    @SerializedName("spam_complaints")
+    private int spamComplaints;
+
+    private int opens;
+
+    @SerializedName("unique_opens")
+    private int uniqueOpens;
+
+    private int clicks;
+
+    @SerializedName("unique_clicks")
+    private int uniqueClicks;
+
+    private int unsubscribes;
+
+    public int getInjections() {
+        return injections;
+    }
+
+    public int getDeliveries() {
+        return deliveries;
+    }
+
+    public int getBounces() {
+        return bounces;
+    }
+
+    public int getSpamComplaints() {
+        return spamComplaints;
+    }
+
+    public int getOpens() {
+        return opens;
+    }
+
+    public int getUniqueOpens() {
+        return uniqueOpens;
+    }
+
+    public int getClicks() {
+        return clicks;
+    }
+
+    public int getUniqueClicks() {
+        return uniqueClicks;
+    }
+
+    public int getUnsubscribes() {
+        return unsubscribes;
+    }
+
+    @Override
+    public String toString() {
+        return "CampaignStats{injections=" + injections
+                + ", deliveries=" + deliveries
+                + ", bounces=" + bounces
+                + ", spamComplaints=" + spamComplaints
+                + ", opens=" + opens
+                + ", uniqueOpens=" + uniqueOpens
+                + ", clicks=" + clicks
+                + ", uniqueClicks=" + uniqueClicks
+                + ", unsubscribes=" + unsubscribes + '}';
+    }
+}
diff --git a/src/main/java/com/lettr/services/campaigns/model/CampaignStatus.java b/src/main/java/com/lettr/services/campaigns/model/CampaignStatus.java
new file mode 100644
index 0000000..34497cb
--- /dev/null
+++ b/src/main/java/com/lettr/services/campaigns/model/CampaignStatus.java
@@ -0,0 +1,17 @@
+package com.lettr.services.campaigns.model;
+
+import com.google.gson.annotations.SerializedName;
+
+/**
+ * Lifecycle status of a campaign. Wire values are defined by {@code @SerializedName};
+ * use {@link com.lettr.core.util.WireValues#of(Enum)} to retrieve them.
+ */
+public enum CampaignStatus {
+    @SerializedName("draft") DRAFT,
+    @SerializedName("scheduled") SCHEDULED,
+    @SerializedName("preparing") PREPARING,
+    @SerializedName("in_review") IN_REVIEW,
+    @SerializedName("sending") SENDING,
+    @SerializedName("sent") SENT,
+    @SerializedName("failed") FAILED
+}
diff --git a/src/main/java/com/lettr/services/campaigns/model/CampaignView.java b/src/main/java/com/lettr/services/campaigns/model/CampaignView.java
new file mode 100644
index 0000000..104699a
--- /dev/null
+++ b/src/main/java/com/lettr/services/campaigns/model/CampaignView.java
@@ -0,0 +1,126 @@
+package com.lettr.services.campaigns.model;
+
+import com.google.gson.annotations.SerializedName;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
+/**
+ * Represents a single campaign as returned by the API, with embedded engagement
+ * stats. The {@code htmlContent} field is only populated by
+ * {@link com.lettr.services.campaigns.Campaigns#get(String)}; it is {@code null}
+ * on list, send, schedule, and unschedule responses.
+ */
+public class CampaignView {
+
+    private String id;
+    private String name;
+    private String subject;
+
+    @SerializedName("from_email")
+    private String fromEmail;
+
+    @SerializedName("from_name")
+    private String fromName;
+
+    @SerializedName("reply_to")
+    private String replyTo;
+
+    private CampaignStatus status;
+
+    @SerializedName("scheduled_at")
+    private String scheduledAt;
+
+    @SerializedName("total_recipients")
+    private Integer totalRecipients;
+
+    @SerializedName("sent_count")
+    private int sentCount;
+
+    @SerializedName("sent_at")
+    private String sentAt;
+
+    @SerializedName("created_at")
+    private String createdAt;
+
+    @SerializedName("html_content")
+    private String htmlContent;
+
+    private CampaignStats stats;
+
+    @Nonnull
+    public String getId() {
+        return id;
+    }
+
+    @Nonnull
+    public String getName() {
+        return name;
+    }
+
+    @Nullable
+    public String getSubject() {
+        return subject;
+    }
+
+    @Nullable
+    public String getFromEmail() {
+        return fromEmail;
+    }
+
+    @Nullable
+    public String getFromName() {
+        return fromName;
+    }
+
+    @Nullable
+    public String getReplyTo() {
+        return replyTo;
+    }
+
+    @Nonnull
+    public CampaignStatus getStatus() {
+        return status;
+    }
+
+    @Nullable
+    public String getScheduledAt() {
+        return scheduledAt;
+    }
+
+    @Nullable
+    public Integer getTotalRecipients() {
+        return totalRecipients;
+    }
+
+    public int getSentCount() {
+        return sentCount;
+    }
+
+    @Nullable
+    public String getSentAt() {
+        return sentAt;
+    }
+
+    @Nonnull
+    public String getCreatedAt() {
+        return createdAt;
+    }
+
+    /** Rendered HTML content. Only present on {@code get}; {@code null} otherwise. */
+    @Nullable
+    public String getHtmlContent() {
+        return htmlContent;
+    }
+
+    @Nonnull
+    public CampaignStats getStats() {
+        return stats;
+    }
+
+    @Override
+    public String toString() {
+        return "CampaignView{id='" + id + "', name='" + name + "', status=" + status
+                + ", sentCount=" + sentCount + '}';
+    }
+}
diff --git a/src/main/java/com/lettr/services/campaigns/model/ListCampaignEventsParams.java b/src/main/java/com/lettr/services/campaigns/model/ListCampaignEventsParams.java
new file mode 100644
index 0000000..8f41773
--- /dev/null
+++ b/src/main/java/com/lettr/services/campaigns/model/ListCampaignEventsParams.java
@@ -0,0 +1,105 @@
+package com.lettr.services.campaigns.model;
+
+import com.lettr.core.util.WireValues;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+/**
+ * Parameters for listing campaign engagement events. All fields are optional.
+ */
+public class ListCampaignEventsParams {
+
+    private final CampaignEventType eventType;
+    private final String email;
+    private final String startDate;
+    private final String endDate;
+    private final Integer limit;
+    private final String cursor;
+
+    private ListCampaignEventsParams(Builder builder) {
+        this.eventType = builder.eventType;
+        this.email = builder.email;
+        this.startDate = builder.startDate;
+        this.endDate = builder.endDate;
+        this.limit = builder.limit;
+        this.cursor = builder.cursor;
+    }
+
+    @Nonnull
+    public static Builder builder() {
+        return new Builder();
+    }
+
+    @Nonnull
+    public Map<String, String> toQueryParams() {
+        Map<String, String> params = new LinkedHashMap<>();
+        if (eventType != null) params.put("event_type", WireValues.of(eventType));
+        if (email != null) params.put("email", email);
+        if (startDate != null) params.put("start_date", startDate);
+        if (endDate != null) params.put("end_date", endDate);
+        if (limit != null) params.put("limit", limit.toString());
+        if (cursor != null) params.put("cursor", cursor);
+        return params;
+    }
+
+    public static class Builder {
+        private CampaignEventType eventType;
+        private String email;
+        private String startDate;
+        private String endDate;
+        private Integer limit;
+        private String cursor;
+
+        private Builder() {}
+
+        /** <b>(optional)</b> Filters by event type. */
+        @Nonnull
+        public Builder eventType(@Nullable CampaignEventType eventType) {
+            this.eventType = eventType;
+            return this;
+        }
+
+        /** <b>(optional)</b> Filters by recipient email address. */
+        @Nonnull
+        public Builder email(@Nullable String email) {
+            this.email = email;
+            return this;
+        }
+
+        /** <b>(optional)</b> Only events at or after this time (ISO 8601). A date-only value is treated as the start of that day in UTC. */
+        @Nonnull
+        public Builder startDate(@Nullable String startDate) {
+            this.startDate = startDate;
+            return this;
+        }
+
+        /** <b>(optional)</b> Only events at or before this time, inclusive (ISO 8601). A date-only value covers the whole of that day in UTC. */
+        @Nonnull
+        public Builder endDate(@Nullable String endDate) {
+            this.endDate = endDate;
+            return this;
+        }
+
+        /** <b>(optional)</b> Max events per page (1–100, default 25). */
+        @Nonnull
+        public Builder limit(@Nullable Integer limit) {
+            this.limit = limit;
+            return this;
+        }
+
+        /** <b>(optional)</b> Pagination cursor from a previous response. */
+        @Nonnull
+        public Builder cursor(@Nullable String cursor) {
+            this.cursor = cursor;
+            return this;
+        }
+
+        @Nonnull
+        public ListCampaignEventsParams build() {
+            return new ListCampaignEventsParams(this);
+        }
+    }
+}
diff --git a/src/main/java/com/lettr/services/campaigns/model/ListCampaignEventsResponse.java b/src/main/java/com/lettr/services/campaigns/model/ListCampaignEventsResponse.java
new file mode 100644
index 0000000..cfb7d89
--- /dev/null
+++ b/src/main/java/com/lettr/services/campaigns/model/ListCampaignEventsResponse.java
@@ -0,0 +1,41 @@
+package com.lettr.services.campaigns.model;
+
+import com.google.gson.annotations.SerializedName;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * Response from listing campaign engagement events. Uses cursor-based pagination:
+ * keep requesting with {@link #getNextCursor()} until it is {@code null}.
+ *
+ * <p>When a filter is applied, a page may come back with an empty {@code events}
+ * list <b>and</b> a non-null {@code nextCursor} — that means more pages remain,
+ * not that there are no matching events, so continue paginating until
+ * {@code nextCursor} is {@code null}.</p>
+ */
+public class ListCampaignEventsResponse {
+
+    private List<CampaignEvent> events;
+
+    @SerializedName("next_cursor")
+    private String nextCursor;
+
+    @Nonnull
+    public List<CampaignEvent> getEvents() {
+        return events != null ? events : Collections.emptyList();
+    }
+
+    /** Cursor for the next page, or {@code null} if there are no more results. */
+    @Nullable
+    public String getNextCursor() {
+        return nextCursor;
+    }
+
+    @Override
+    public String toString() {
+        return "ListCampaignEventsResponse{events=" + events + ", nextCursor='" + nextCursor + "'}";
+    }
+}
diff --git a/src/main/java/com/lettr/services/campaigns/model/ListCampaignsParams.java b/src/main/java/com/lettr/services/campaigns/model/ListCampaignsParams.java
new file mode 100644
index 0000000..5de85b9
--- /dev/null
+++ b/src/main/java/com/lettr/services/campaigns/model/ListCampaignsParams.java
@@ -0,0 +1,70 @@
+package com.lettr.services.campaigns.model;
+
+import com.lettr.core.model.PageParams;
+import com.lettr.core.util.WireValues;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+/**
+ * Parameters for listing campaigns. All fields are optional. Composes
+ * {@link PageParams} for {@code page} / {@code per_page} and adds a
+ * {@code status} filter.
+ */
+public class ListCampaignsParams {
+
+    private final PageParams pageParams;
+    private final CampaignStatus status;
+
+    private ListCampaignsParams(Builder builder) {
+        this.pageParams = builder.pageParams.build();
+        this.status = builder.status;
+    }
+
+    @Nonnull
+    public static Builder builder() {
+        return new Builder();
+    }
+
+    @Nonnull
+    public Map<String, String> toQueryParams() {
+        Map<String, String> params = new LinkedHashMap<>(pageParams.toQueryParams());
+        if (status != null) params.put("status", WireValues.of(status));
+        return params;
+    }
+
+    public static class Builder {
+        private final PageParams.Builder pageParams = PageParams.builder();
+        private CampaignStatus status;
+
+        private Builder() {}
+
+        /** <b>(optional)</b> Page number (min 1, default 1). */
+        @Nonnull
+        public Builder page(@Nullable Integer page) {
+            pageParams.page(page);
+            return this;
+        }
+
+        /** <b>(optional)</b> Items per page (1–100, default 20). */
+        @Nonnull
+        public Builder perPage(@Nullable Integer perPage) {
+            pageParams.perPage(perPage);
+            return this;
+        }
+
+        /** <b>(optional)</b> Filters by campaign status. */
+        @Nonnull
+        public Builder status(@Nullable CampaignStatus status) {
+            this.status = status;
+            return this;
+        }
+
+        @Nonnull
+        public ListCampaignsParams build() {
+            return new ListCampaignsParams(this);
+        }
+    }
+}
diff --git a/src/main/java/com/lettr/services/campaigns/model/ListCampaignsResponse.java b/src/main/java/com/lettr/services/campaigns/model/ListCampaignsResponse.java
new file mode 100644
index 0000000..d9c2812
--- /dev/null
+++ b/src/main/java/com/lettr/services/campaigns/model/ListCampaignsResponse.java
@@ -0,0 +1,31 @@
+package com.lettr.services.campaigns.model;
+
+import com.lettr.core.model.OffsetPagination;
+
+import javax.annotation.Nonnull;
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * Response from listing campaigns: a page of campaigns plus pagination metadata.
+ */
+public class ListCampaignsResponse {
+
+    private List<CampaignView> campaigns;
+    private OffsetPagination pagination;
+
+    @Nonnull
+    public List<CampaignView> getCampaigns() {
+        return campaigns != null ? campaigns : Collections.emptyList();
+    }
+
+    @Nonnull
+    public OffsetPagination getPagination() {
+        return pagination;
+    }
+
+    @Override
+    public String toString() {
+        return "ListCampaignsResponse{campaigns=" + campaigns + ", pagination=" + pagination + '}';
+    }
+}
diff --git a/src/main/java/com/lettr/services/campaigns/model/ScheduleCampaignOptions.java b/src/main/java/com/lettr/services/campaigns/model/ScheduleCampaignOptions.java
new file mode 100644
index 0000000..f1a5045
--- /dev/null
+++ b/src/main/java/com/lettr/services/campaigns/model/ScheduleCampaignOptions.java
@@ -0,0 +1,34 @@
+package com.lettr.services.campaigns.model;
+
+import com.google.gson.annotations.SerializedName;
+import com.lettr.core.util.Args;
+
+import javax.annotation.Nonnull;
+
+/**
+ * Request body for scheduling (or rescheduling) a campaign.
+ */
+public class ScheduleCampaignOptions {
+
+    @SerializedName("scheduled_at")
+    private final String scheduledAt;
+
+    private ScheduleCampaignOptions(String scheduledAt) {
+        this.scheduledAt = scheduledAt;
+    }
+
+    /**
+     * @param scheduledAt future delivery time (ISO 8601). Include a timezone offset
+     *                    (e.g. {@code +02:00} or {@code Z}); a value without an offset
+     *                    is interpreted as UTC. Must be in the future.
+     */
+    @Nonnull
+    public static ScheduleCampaignOptions of(@Nonnull String scheduledAt) {
+        return new ScheduleCampaignOptions(Args.requireNonEmpty("scheduledAt", scheduledAt));
+    }
+
+    @Nonnull
+    public String getScheduledAt() {
+        return scheduledAt;
+    }
+}
diff --git a/src/main/java/com/lettr/services/emails/Emails.java b/src/main/java/com/lettr/services/emails/Emails.java
index 4b73832..843cb30 100644
--- a/src/main/java/com/lettr/services/emails/Emails.java
+++ b/src/main/java/com/lettr/services/emails/Emails.java
@@ -1,6 +1,7 @@
 package com.lettr.services.emails;
 
 import com.lettr.core.exception.LettrException;
+import com.lettr.core.net.HttpClient;
 import com.lettr.services.BaseService;
 import com.lettr.services.emails.model.*;
 
@@ -100,7 +101,7 @@ public GetEmailResponse get(@Nonnull String requestId, @Nullable String from, @N
             if (from != null) params.put("from", from);
             if (to != null) params.put("to", to);
         }
-        return httpClient.get("/emails/" + requestId, params, GetEmailResponse.class);
+        return httpClient.get("/emails/" + HttpClient.encodePathSegment(requestId), params, GetEmailResponse.class);
     }
 
     /**
@@ -128,7 +129,7 @@ public ScheduledEmail getScheduled(@Nonnull String transmissionId) throws LettrE
         if (transmissionId == null || transmissionId.isEmpty()) {
             throw new IllegalArgumentException("transmissionId is required");
         }
-        return httpClient.get("/emails/scheduled/" + transmissionId, null, ScheduledEmail.class);
+        return httpClient.get("/emails/scheduled/" + HttpClient.encodePathSegment(transmissionId), null, ScheduledEmail.class);
     }
 
     /**
@@ -142,6 +143,6 @@ public void cancelScheduled(@Nonnull String transmissionId) throws LettrExceptio
         if (transmissionId == null || transmissionId.isEmpty()) {
             throw new IllegalArgumentException("transmissionId is required");
         }
-        httpClient.delete("/emails/scheduled/" + transmissionId);
+        httpClient.delete("/emails/scheduled/" + HttpClient.encodePathSegment(transmissionId));
     }
 }
diff --git a/src/main/resources/com/lettr/version.properties b/src/main/resources/com/lettr/version.properties
new file mode 100644
index 0000000..a50bf5c
--- /dev/null
+++ b/src/main/resources/com/lettr/version.properties
@@ -0,0 +1 @@
+version=${version}
diff --git a/src/test/java/com/lettr/LettrTest.java b/src/test/java/com/lettr/LettrTest.java
index 8c84874..f76d816 100644
--- a/src/test/java/com/lettr/LettrTest.java
+++ b/src/test/java/com/lettr/LettrTest.java
@@ -1,5 +1,7 @@
 package com.lettr;
 
+import com.lettr.services.audience.Audience;
+import com.lettr.services.campaigns.Campaigns;
 import com.lettr.services.domains.Domains;
 import com.lettr.services.emails.Emails;
 import com.lettr.services.projects.Projects;
@@ -66,6 +68,20 @@ void systemReturnsServiceInstance() {
         assertNotNull(system);
     }
 
+    @Test
+    void audienceReturnsServiceInstance() {
+        Lettr lettr = new Lettr("test-api-key");
+        Audience audience = lettr.audience();
+        assertNotNull(audience);
+    }
+
+    @Test
+    void campaignsReturnsServiceInstance() {
+        Lettr lettr = new Lettr("test-api-key");
+        Campaigns campaigns = lettr.campaigns();
+        assertNotNull(campaigns);
+    }
+
     @Test
     void servicesAreNewInstancesEachCall() {
         Lettr lettr = new Lettr("test-api-key");
@@ -75,5 +91,7 @@ void servicesAreNewInstancesEachCall() {
         assertNotSame(lettr.templates(), lettr.templates());
         assertNotSame(lettr.projects(), lettr.projects());
         assertNotSame(lettr.system(), lettr.system());
+        assertNotSame(lettr.audience(), lettr.audience());
+        assertNotSame(lettr.campaigns(), lettr.campaigns());
     }
 }
diff --git a/src/test/java/com/lettr/core/net/HttpClientTest.java b/src/test/java/com/lettr/core/net/HttpClientTest.java
index 6d32c99..3375dce 100644
--- a/src/test/java/com/lettr/core/net/HttpClientTest.java
+++ b/src/test/java/com/lettr/core/net/HttpClientTest.java
@@ -17,6 +17,28 @@ void constructorAcceptsApiKey() {
         assertNotNull(client);
     }
 
+    @Test
+    void encodePathSegmentEscapesReservedCharacters() {
+        // Reserved path characters must be percent-encoded so callers can safely
+        // interpolate arbitrary identifiers.
+        assertEquals("foo%2Fbar", HttpClient.encodePathSegment("foo/bar"));
+        assertEquals("foo%3Fbar", HttpClient.encodePathSegment("foo?bar"));
+        assertEquals("foo%23bar", HttpClient.encodePathSegment("foo#bar"));
+        assertEquals("hello%20world", HttpClient.encodePathSegment("hello world"));
+        assertEquals("100%25", HttpClient.encodePathSegment("100%"));
+    }
+
+    @Test
+    void encodePathSegmentLeavesUuidUnchanged() {
+        String uuid = "0193e6a8-1f3a-7c2a-b9e2-1aa1d2e5d3f0";
+        assertEquals(uuid, HttpClient.encodePathSegment(uuid));
+    }
+
+    @Test
+    void encodePathSegmentHandlesNull() {
+        assertEquals("", HttpClient.encodePathSegment(null));
+    }
+
     @Test
     void gsonInstanceAvailable() {
         HttpClient client = new HttpClient("test-key");
diff --git a/src/test/java/com/lettr/core/util/ArgsTest.java b/src/test/java/com/lettr/core/util/ArgsTest.java
new file mode 100644
index 0000000..b1c0629
--- /dev/null
+++ b/src/test/java/com/lettr/core/util/ArgsTest.java
@@ -0,0 +1,37 @@
+package com.lettr.core.util;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class ArgsTest {
+
+    @Test
+    void requireNonEmptyAcceptsNonEmptyAndReturnsValue() {
+        assertEquals("hi", Args.requireNonEmpty("name", "hi"));
+    }
+
+    @Test
+    void requireNonEmptyRejectsNullAndEmpty() {
+        IllegalArgumentException ex1 = assertThrows(IllegalArgumentException.class,
+                () -> Args.requireNonEmpty("listId", null));
+        assertEquals("listId is required", ex1.getMessage());
+
+        IllegalArgumentException ex2 = assertThrows(IllegalArgumentException.class,
+                () -> Args.requireNonEmpty("listId", ""));
+        assertEquals("listId is required", ex2.getMessage());
+    }
+
+    @Test
+    void requireNonNullAcceptsAndReturnsValue() {
+        Object o = new Object();
+        assertSame(o, Args.requireNonNull("options", o));
+    }
+
+    @Test
+    void requireNonNullRejectsNull() {
+        IllegalArgumentException ex = assertThrows(IllegalArgumentException.class,
+                () -> Args.requireNonNull("options", null));
+        assertEquals("options is required", ex.getMessage());
+    }
+}
diff --git a/src/test/java/com/lettr/core/util/WireValuesTest.java b/src/test/java/com/lettr/core/util/WireValuesTest.java
new file mode 100644
index 0000000..081a0c2
--- /dev/null
+++ b/src/test/java/com/lettr/core/util/WireValuesTest.java
@@ -0,0 +1,34 @@
+package com.lettr.core.util;
+
+import com.google.gson.annotations.SerializedName;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class WireValuesTest {
+
+    enum Annotated {
+        @SerializedName("kebab-case") KEBAB,
+        @SerializedName("snake_case") SNAKE
+    }
+
+    enum Bare {
+        FALLBACK
+    }
+
+    @Test
+    void returnsSerializedNameValue() {
+        assertEquals("kebab-case", WireValues.of(Annotated.KEBAB));
+        assertEquals("snake_case", WireValues.of(Annotated.SNAKE));
+    }
+
+    @Test
+    void fallsBackToEnumNameWhenUnannotated() {
+        assertEquals("FALLBACK", WireValues.of(Bare.FALLBACK));
+    }
+
+    @Test
+    void rejectsNull() {
+        assertThrows(IllegalArgumentException.class, () -> WireValues.of(null));
+    }
+}
diff --git a/src/test/java/com/lettr/services/campaigns/CampaignsTest.java b/src/test/java/com/lettr/services/campaigns/CampaignsTest.java
new file mode 100644
index 0000000..a586926
--- /dev/null
+++ b/src/test/java/com/lettr/services/campaigns/CampaignsTest.java
@@ -0,0 +1,229 @@
+package com.lettr.services.campaigns;
+
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import com.lettr.core.util.WireValues;
+import com.lettr.services.campaigns.model.*;
+import org.junit.jupiter.api.Test;
+
+import java.util.Map;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class CampaignsTest {
+
+    private final Gson gson = new GsonBuilder()
+            .setDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSXXX")
+            .create();
+
+    @Test
+    void campaignViewDeserializesWithStats() {
+        String json = "{"
+                + "\"id\":\"0193e6a8-1f3a-7c2a-b9e2-1aa1d2e5d3f0\","
+                + "\"name\":\"Spring Newsletter\","
+                + "\"subject\":\"Hello\","
+                + "\"from_email\":\"news@example.com\","
+                + "\"from_name\":\"Example\","
+                + "\"reply_to\":null,"
+                + "\"status\":\"sent\","
+                + "\"scheduled_at\":null,"
+                + "\"total_recipients\":1000,"
+                + "\"sent_count\":980,"
+                + "\"sent_at\":\"2026-05-20T10:00:00+00:00\","
+                + "\"created_at\":\"2026-05-19T08:00:00+00:00\","
+                + "\"html_content\":\"<p>Hi</p>\","
+                + "\"stats\":{\"injections\":1000,\"deliveries\":980,\"bounces\":20,"
+                + "\"spam_complaints\":1,\"opens\":500,\"unique_opens\":400,"
+                + "\"clicks\":120,\"unique_clicks\":90,\"unsubscribes\":5}"
+                + "}";
+
+        CampaignView c = gson.fromJson(json, CampaignView.class);
+
+        assertEquals("0193e6a8-1f3a-7c2a-b9e2-1aa1d2e5d3f0", c.getId());
+        assertEquals("Spring Newsletter", c.getName());
+        assertEquals("news@example.com", c.getFromEmail());
+        assertNull(c.getReplyTo());
+        assertEquals(CampaignStatus.SENT, c.getStatus());
+        assertEquals(Integer.valueOf(1000), c.getTotalRecipients());
+        assertEquals(980, c.getSentCount());
+        assertEquals("<p>Hi</p>", c.getHtmlContent());
+
+        CampaignStats stats = c.getStats();
+        assertNotNull(stats);
+        assertEquals(980, stats.getDeliveries());
+        assertEquals(1, stats.getSpamComplaints());
+        assertEquals(400, stats.getUniqueOpens());
+        assertEquals(90, stats.getUniqueClicks());
+    }
+
+    @Test
+    void campaignViewWithoutHtmlContentLeavesItNull() {
+        String json = "{\"id\":\"abc\",\"name\":\"Draft\",\"status\":\"draft\","
+                + "\"total_recipients\":null,\"sent_count\":0,"
+                + "\"created_at\":\"2026-05-19T08:00:00+00:00\","
+                + "\"stats\":{\"injections\":0,\"deliveries\":0,\"bounces\":0,"
+                + "\"spam_complaints\":0,\"opens\":0,\"unique_opens\":0,"
+                + "\"clicks\":0,\"unique_clicks\":0,\"unsubscribes\":0}}";
+
+        CampaignView c = gson.fromJson(json, CampaignView.class);
+
+        assertEquals(CampaignStatus.DRAFT, c.getStatus());
+        assertNull(c.getHtmlContent());
+        assertNull(c.getTotalRecipients());
+        assertEquals(0, c.getSentCount());
+    }
+
+    @Test
+    void listCampaignsResponseDeserializes() {
+        String json = "{\"campaigns\":[{\"id\":\"abc\",\"name\":\"C1\",\"status\":\"draft\","
+                + "\"sent_count\":0,\"created_at\":\"2026-05-19T08:00:00+00:00\","
+                + "\"stats\":{\"injections\":0,\"deliveries\":0,\"bounces\":0,"
+                + "\"spam_complaints\":0,\"opens\":0,\"unique_opens\":0,"
+                + "\"clicks\":0,\"unique_clicks\":0,\"unsubscribes\":0}}],"
+                + "\"pagination\":{\"total\":1,\"per_page\":20,\"current_page\":1,\"last_page\":1}}";
+
+        ListCampaignsResponse response = gson.fromJson(json, ListCampaignsResponse.class);
+
+        assertEquals(1, response.getCampaigns().size());
+        assertEquals("C1", response.getCampaigns().get(0).getName());
+        assertEquals(20, response.getPagination().getPerPage());
+        assertEquals(1, response.getPagination().getLastPage());
+    }
+
+    @Test
+    void listCampaignsResponseMissingCampaignsReturnsEmptyList() {
+        ListCampaignsResponse response = gson.fromJson("{\"pagination\":{\"total\":0,\"per_page\":20,\"current_page\":1,\"last_page\":0}}", ListCampaignsResponse.class);
+        assertNotNull(response.getCampaigns());
+        assertTrue(response.getCampaigns().isEmpty());
+    }
+
+    @Test
+    void campaignEventAndResponseDeserialize() {
+        String json = "{\"events\":[{\"event_id\":\"evt_1\",\"event_type\":\"click\","
+                + "\"email\":\"user@example.com\",\"timestamp\":\"2026-05-20T10:05:00+00:00\","
+                + "\"bounce_class\":null,\"reason\":null,"
+                + "\"target_link_url\":\"https://example.com\",\"user_agent\":\"Mozilla\"}],"
+                + "\"next_cursor\":\"cursor-123\"}";
+
+        ListCampaignEventsResponse response = gson.fromJson(json, ListCampaignEventsResponse.class);
+
+        assertEquals(1, response.getEvents().size());
+        CampaignEvent e = response.getEvents().get(0);
+        assertEquals("evt_1", e.getEventId());
+        assertEquals(CampaignEventType.CLICK, e.getEventType());
+        assertEquals("https://example.com", e.getTargetLinkUrl());
+        assertNull(e.getBounceClass());
+        assertEquals("cursor-123", response.getNextCursor());
+    }
+
+    @Test
+    void campaignEventsResponseNullCursorMeansLastPage() {
+        String json = "{\"events\":[],\"next_cursor\":null}";
+
+        ListCampaignEventsResponse response = gson.fromJson(json, ListCampaignEventsResponse.class);
+
+        assertTrue(response.getEvents().isEmpty());
+        assertNull(response.getNextCursor());
+    }
+
+    @Test
+    void campaignEventsResponseMissingEventsReturnsEmptyList() {
+        ListCampaignEventsResponse response = gson.fromJson("{\"next_cursor\":null}", ListCampaignEventsResponse.class);
+        assertNotNull(response.getEvents());
+        assertTrue(response.getEvents().isEmpty());
+    }
+
+    @Test
+    void enumsRoundTripWithWireValues() {
+        assertEquals(CampaignStatus.IN_REVIEW, gson.fromJson("\"in_review\"", CampaignStatus.class));
+        assertEquals("in_review", WireValues.of(CampaignStatus.IN_REVIEW));
+        assertEquals(CampaignEventType.SPAM_COMPLAINT, gson.fromJson("\"spam_complaint\"", CampaignEventType.class));
+        assertEquals("spam_complaint", WireValues.of(CampaignEventType.SPAM_COMPLAINT));
+        assertEquals("list_unsubscribe", WireValues.of(CampaignEventType.LIST_UNSUBSCRIBE));
+    }
+
+    @Test
+    void listCampaignsParamsBuildQueryParams() {
+        Map<String, String> params = ListCampaignsParams.builder()
+                .page(2)
+                .perPage(50)
+                .status(CampaignStatus.SCHEDULED)
+                .build()
+                .toQueryParams();
+
+        assertEquals("2", params.get("page"));
+        assertEquals("50", params.get("per_page"));
+        assertEquals("scheduled", params.get("status"));
+    }
+
+    @Test
+    void listCampaignsParamsOmitsNulls() {
+        Map<String, String> params = ListCampaignsParams.builder().build().toQueryParams();
+        assertTrue(params.isEmpty());
+    }
+
+    @Test
+    void listCampaignEventsParamsBuildQueryParams() {
+        Map<String, String> params = ListCampaignEventsParams.builder()
+                .eventType(CampaignEventType.OPEN)
+                .email("user@example.com")
+                .startDate("2026-05-01")
+                .endDate("2026-05-31")
+                .limit(100)
+                .cursor("abc")
+                .build()
+                .toQueryParams();
+
+        assertEquals("open", params.get("event_type"));
+        assertEquals("user@example.com", params.get("email"));
+        assertEquals("2026-05-01", params.get("start_date"));
+        assertEquals("2026-05-31", params.get("end_date"));
+        assertEquals("100", params.get("limit"));
+        assertEquals("abc", params.get("cursor"));
+    }
+
+    @Test
+    void scheduleOptionsRequiresScheduledAt() {
+        assertThrows(IllegalArgumentException.class, () -> ScheduleCampaignOptions.of(null));
+        assertThrows(IllegalArgumentException.class, () -> ScheduleCampaignOptions.of(""));
+        assertEquals("2026-06-01T09:00:00+00:00",
+                ScheduleCampaignOptions.of("2026-06-01T09:00:00+00:00").getScheduledAt());
+    }
+
+    @Test
+    void getRequiresCampaignId() {
+        Campaigns svc = new Campaigns("test-key");
+        assertThrows(IllegalArgumentException.class, () -> svc.get(null));
+        assertThrows(IllegalArgumentException.class, () -> svc.get(""));
+    }
+
+    @Test
+    void listEventsRequiresCampaignId() {
+        Campaigns svc = new Campaigns("test-key");
+        assertThrows(IllegalArgumentException.class, () -> svc.listEvents(null));
+        assertThrows(IllegalArgumentException.class, () -> svc.listEvents(""));
+    }
+
+    @Test
+    void sendRequiresCampaignId() {
+        Campaigns svc = new Campaigns("test-key");
+        assertThrows(IllegalArgumentException.class, () -> svc.send(null));
+        assertThrows(IllegalArgumentException.class, () -> svc.send(""));
+    }
+
+    @Test
+    void unscheduleRequiresCampaignId() {
+        Campaigns svc = new Campaigns("test-key");
+        assertThrows(IllegalArgumentException.class, () -> svc.unschedule(null));
+        assertThrows(IllegalArgumentException.class, () -> svc.unschedule(""));
+    }
+
+    @Test
+    void scheduleRequiresCampaignIdAndOptions() {
+        Campaigns svc = new Campaigns("test-key");
+        ScheduleCampaignOptions valid = ScheduleCampaignOptions.of("2026-06-01T09:00:00+00:00");
+        assertThrows(IllegalArgumentException.class, () -> svc.schedule(null, valid));
+        assertThrows(IllegalArgumentException.class, () -> svc.schedule("", valid));
+        assertThrows(IllegalArgumentException.class, () -> svc.schedule("campaign-id", null));
+    }
+}