diff --git a/server/StudySharp.API/Controllers/CourseController.cs b/server/StudySharp.API/Controllers/CourseController.cs
index 3337ebc..51b4100 100644
--- a/server/StudySharp.API/Controllers/CourseController.cs
+++ b/server/StudySharp.API/Controllers/CourseController.cs
@@ -1,6 +1,7 @@
 using System.Threading.Tasks;
 using AutoMapper;
 using MediatR;
+using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Mvc;
 using StudySharp.API.Requests.Courses;
 using StudySharp.API.Requests.PracticalBlocks;
diff --git a/server/StudySharp.ApplicationServices/Commands/AddCourseCommand.cs b/server/StudySharp.ApplicationServices/Commands/AddCourseCommand.cs
index f0fd2e6..5cc2a61 100644
--- a/server/StudySharp.ApplicationServices/Commands/AddCourseCommand.cs
+++ b/server/StudySharp.ApplicationServices/Commands/AddCourseCommand.cs
@@ -1,10 +1,12 @@
 using System.Threading;
 using System.Threading.Tasks;
+using FluentValidation;
 using MediatR;
 using Microsoft.EntityFrameworkCore;
 using StudySharp.Domain.Constants;
 using StudySharp.Domain.General;
 using StudySharp.Domain.Models;
+using StudySharp.Domain.ValidationRules;
 using StudySharp.DomainServices;
 
 namespace StudySharp.ApplicationServices.Commands
@@ -15,6 +17,24 @@ public sealed class AddCourseCommand : IRequest<OperationResult>
         public int TeacherId { get; set; }
     }
 
+    public class AddCourseCommandValidator : AbstractValidator<AddCourseCommand>
+    {
+        public AddCourseCommandValidator(ICourseRules rules)
+        {
+            RuleFor(_ => new { _.Name, _.TeacherId })
+                .NotEmpty()
+                .WithMessage(string.Format(ErrorConstants.FieldIsRequired, nameof(Course.Name)))
+                .MustAsync((courseTeacherAndName, token) => rules.IsNameUniqueAsync(courseTeacherAndName.Name, courseTeacherAndName.TeacherId, token))
+                .WithMessage(_ => string.Format(ErrorConstants.EntityAlreadyExists, nameof(Course), nameof(Course.Name), _.Name));
+
+            RuleFor(_ => _.TeacherId)
+                .NotEmpty()
+                .WithMessage(string.Format(ErrorConstants.FieldIsRequired, nameof(Course.TeacherId)))
+                .MustAsync(rules.IsTeacherIdExistAsync)
+                .WithMessage(_ => string.Format(ErrorConstants.EntityNotFound, nameof(Teacher), nameof(Teacher.Id), _.TeacherId));
+        }
+    }
+
     public sealed class AddCourseCommandHandler : IRequestHandler<AddCourseCommand, OperationResult>
     {
         private readonly StudySharpDbContext _context;
@@ -26,9 +46,7 @@ public AddCourseCommandHandler(StudySharpDbContext sharpDbContext)
 
         public async Task<OperationResult> Handle(AddCourseCommand request, CancellationToken cancellationToken)
         {
-            if (await _context.Courses.AnyAsync(
-                _ => _.Name.ToLower().Equals(request.Name.ToLower()) && _.TeacherId == request.TeacherId,
-                cancellationToken))
+            if (await _context.Courses.AnyAsync(_ => _.Name.ToLower().Equals(request.Name.ToLower()) && _.TeacherId == request.TeacherId))
             {
                 return OperationResult.Fail(string.Format(ErrorConstants.EntityAlreadyExists, nameof(Course), nameof(Course.Name), request.Name));
             }
diff --git a/server/StudySharp.ApplicationServices/Commands/RemoveCourseByIdCommand.cs b/server/StudySharp.ApplicationServices/Commands/RemoveCourseByIdCommand.cs
index 0262e8a..b77a991 100644
--- a/server/StudySharp.ApplicationServices/Commands/RemoveCourseByIdCommand.cs
+++ b/server/StudySharp.ApplicationServices/Commands/RemoveCourseByIdCommand.cs
@@ -1,9 +1,11 @@
 using System.Threading;
 using System.Threading.Tasks;
+using FluentValidation;
 using MediatR;
 using StudySharp.Domain.Constants;
 using StudySharp.Domain.General;
 using StudySharp.Domain.Models;
+using StudySharp.Domain.ValidationRules;
 using StudySharp.DomainServices;
 
 namespace StudySharp.ApplicationServices.Commands
@@ -13,6 +15,16 @@ public sealed class RemoveCourseByIdCommand : IRequest<OperationResult>
         public int Id { get; set; }
     }
 
+    public class RemoveCourseByIdCommandValidator : AbstractValidator<RemoveCourseByIdCommand>
+    {
+        public RemoveCourseByIdCommandValidator(ICourseRules rules)
+        {
+            RuleFor(_ => _.Id)
+                .MustAsync(rules.IsCourseIdExistAsync)
+                .WithMessage(_ => string.Format(ErrorConstants.EntityNotFound, nameof(Course), nameof(Course.Id), _.Id));
+        }
+    }
+
     public sealed class RemoveCourseByIdCommandHandler : IRequestHandler<RemoveCourseByIdCommand, OperationResult>
     {
         private readonly StudySharpDbContext _context;
@@ -24,12 +36,7 @@ public RemoveCourseByIdCommandHandler(StudySharpDbContext sharpDbContext)
 
         public async Task<OperationResult> Handle(RemoveCourseByIdCommand request, CancellationToken cancellationToken)
         {
-            var course = await _context.Courses.FindAsync(request.Id, cancellationToken);
-            if (course == null)
-            {
-                return OperationResult.Fail(string.Format(ErrorConstants.EntityNotFound, nameof(Course), nameof(Course.Name), request.Id));
-            }
-
+            var course = await _context.Courses.FindAsync(request.Id);
             _context.Courses.Remove(course);
             await _context.SaveChangesAsync(cancellationToken);
             return OperationResult.Ok();
diff --git a/server/StudySharp.ApplicationServices/Commands/UpdateCourseCommand.cs b/server/StudySharp.ApplicationServices/Commands/UpdateCourseCommand.cs
index 4b0d390..debd962 100644
--- a/server/StudySharp.ApplicationServices/Commands/UpdateCourseCommand.cs
+++ b/server/StudySharp.ApplicationServices/Commands/UpdateCourseCommand.cs
@@ -1,10 +1,12 @@
 using System.Threading;
 using System.Threading.Tasks;
+using FluentValidation;
 using MediatR;
 using Microsoft.EntityFrameworkCore;
 using StudySharp.Domain.Constants;
 using StudySharp.Domain.General;
 using StudySharp.Domain.Models;
+using StudySharp.Domain.ValidationRules;
 using StudySharp.DomainServices;
 
 namespace StudySharp.ApplicationServices.Commands
@@ -16,6 +18,28 @@ public class UpdateCourseCommand : IRequest<OperationResult>
         public int TeacherId { get; set; }
     }
 
+    public partial class UpdateCourseCommandValidator : AbstractValidator<UpdateCourseCommand>
+    {
+        public UpdateCourseCommandValidator(ICourseRules rules)
+        {
+            RuleFor(_ => _.Id)
+                .MustAsync(rules.IsCourseIdExistAsync)
+                .WithMessage(_ => string.Format(ErrorConstants.EntityNotFound, nameof(Course), nameof(Course.Id), _.Id));
+
+            RuleFor(_ => new { _.Name, _.TeacherId })
+                .NotEmpty()
+                .WithMessage(string.Format(ErrorConstants.FieldIsRequired, nameof(Course.Name)))
+                .MustAsync((courseTeacherAndName, token) => rules.IsNameUniqueAsync(courseTeacherAndName.Name, courseTeacherAndName.TeacherId, token))
+                .WithMessage(_ => string.Format(ErrorConstants.EntityAlreadyExists, nameof(Course), nameof(Course.Name), _.Name));
+
+            RuleFor(_ => _.TeacherId)
+                .NotEmpty()
+                .WithMessage(string.Format(ErrorConstants.FieldIsRequired, nameof(Course.TeacherId)))
+                .MustAsync(rules.IsTeacherIdExistAsync)
+                .WithMessage(_ => string.Format(ErrorConstants.EntityNotFound, nameof(Teacher), nameof(Teacher.Id), _.TeacherId));
+        }
+    }
+
     public sealed class UpdateCourseCommandHandler : IRequestHandler<UpdateCourseCommand, OperationResult>
     {
         private readonly StudySharpDbContext _context;
@@ -28,17 +52,6 @@ public UpdateCourseCommandHandler(StudySharpDbContext sharpDbContext)
         public async Task<OperationResult> Handle(UpdateCourseCommand request, CancellationToken cancellationToken)
         {
             var course = await _context.Courses.FirstOrDefaultAsync(_ => _.Id == request.Id, cancellationToken);
-            if (course == null)
-            {
-                return OperationResult.Fail(string.Format(ErrorConstants.EntityNotFound, nameof(Course), nameof(Course.Id), request.Id));
-            }
-
-            var teacherExistent = await _context.Teachers.AnyAsync(_ => _.Id == request.TeacherId, cancellationToken);
-            if (!teacherExistent)
-            {
-                return OperationResult.Fail(string.Format(ErrorConstants.EntityNotFound, nameof(Teacher), nameof(Teacher.Id), request.TeacherId));
-            }
-
             course.Name = request.Name;
             course.TeacherId = request.TeacherId;
 
diff --git a/server/StudySharp.ApplicationServices/Queries/GetCourseByIdQuery.cs b/server/StudySharp.ApplicationServices/Queries/GetCourseByIdQuery.cs
index ca14897..5c06701 100644
--- a/server/StudySharp.ApplicationServices/Queries/GetCourseByIdQuery.cs
+++ b/server/StudySharp.ApplicationServices/Queries/GetCourseByIdQuery.cs
@@ -1,9 +1,11 @@
 using System.Threading;
 using System.Threading.Tasks;
+using FluentValidation;
 using MediatR;
 using StudySharp.Domain.Constants;
 using StudySharp.Domain.General;
 using StudySharp.Domain.Models;
+using StudySharp.Domain.ValidationRules;
 using StudySharp.DomainServices;
 
 namespace StudySharp.ApplicationServices.Queries
@@ -13,6 +15,16 @@ public sealed class GetCourseByIdQuery : IRequest<OperationResult<Course>>
         public int Id { get; set; }
     }
 
+    public partial class GetCourseByIdQueryValidator : AbstractValidator<GetCourseByIdQuery>
+    {
+        public GetCourseByIdQueryValidator(ICourseRules rules)
+        {
+            RuleFor(_ => _.Id)
+                .MustAsync(rules.IsCourseIdExistAsync)
+                .WithMessage(_ => string.Format(ErrorConstants.EntityNotFound, nameof(Course), nameof(Course.Id), _.Id));
+        }
+    }
+
     public sealed class GetCourseByIdQueryHandler : IRequestHandler<GetCourseByIdQuery, OperationResult<Course>>
     {
         private readonly StudySharpDbContext _context;
@@ -24,12 +36,7 @@ public GetCourseByIdQueryHandler(StudySharpDbContext studySharpDbContext)
 
         public async Task<OperationResult<Course>> Handle(GetCourseByIdQuery request, CancellationToken cancellationToken)
         {
-            var course = await _context.Courses.FindAsync(request.Id, cancellationToken);
-            if (course == null)
-            {
-                return OperationResult.Fail<Course>(string.Format(ErrorConstants.EntityNotFound, nameof(Course), nameof(Course.Id), request.Id));
-            }
-
+            var course = await _context.Courses.FindAsync(request.Id);
             return OperationResult.Ok(course);
         }
     }
diff --git a/server/StudySharp.ApplicationServices/Queries/GetCoursesByTeacherIdQuery.cs b/server/StudySharp.ApplicationServices/Queries/GetCoursesByTeacherIdQuery.cs
index 8387543..6292319 100644
--- a/server/StudySharp.ApplicationServices/Queries/GetCoursesByTeacherIdQuery.cs
+++ b/server/StudySharp.ApplicationServices/Queries/GetCoursesByTeacherIdQuery.cs
@@ -2,11 +2,13 @@
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
+using FluentValidation;
 using MediatR;
 using Microsoft.EntityFrameworkCore;
 using StudySharp.Domain.Constants;
 using StudySharp.Domain.General;
 using StudySharp.Domain.Models;
+using StudySharp.Domain.ValidationRules;
 using StudySharp.DomainServices;
 
 namespace StudySharp.ApplicationServices.Queries
@@ -16,6 +18,16 @@ public sealed class GetCoursesByTeacherIdQuery : IRequest<OperationResult<List<C
         public int TeacherId { get; set; }
     }
 
+    public partial class GetCoursesByTeacherIdQueryValidator : AbstractValidator<GetCoursesByTeacherIdQuery>
+    {
+        public GetCoursesByTeacherIdQueryValidator(ICourseRules rules)
+        {
+            RuleFor(_ => _.TeacherId)
+                .MustAsync(rules.IsTeacherIdExistAsync)
+                .WithMessage(_ => string.Format(ErrorConstants.EntityNotFound, nameof(Teacher), nameof(Teacher.Id), _.TeacherId));
+        }
+    }
+
     public sealed class GetCoursesByTeacherIdQueryHandler : IRequestHandler<GetCoursesByTeacherIdQuery, OperationResult<List<Course>>>
     {
         private readonly StudySharpDbContext _context;
@@ -27,12 +39,6 @@ public GetCoursesByTeacherIdQueryHandler(StudySharpDbContext studySharpDbContext
 
         public async Task<OperationResult<List<Course>>> Handle(GetCoursesByTeacherIdQuery request, CancellationToken cancellationToken)
         {
-            var isTeacherExistent = await _context.Teachers.AnyAsync(_ => _.Id == request.TeacherId, cancellationToken);
-            if (!isTeacherExistent)
-            {
-                return OperationResult.Fail<List<Course>>(string.Format(ErrorConstants.EntityNotFound, nameof(Teacher), nameof(Teacher.Id), request.TeacherId));
-            }
-
             var courses = await _context.Courses.Where(_ => _.TeacherId == request.TeacherId).ToListAsync(cancellationToken);
             return OperationResult.Ok(courses);
         }
diff --git a/server/StudySharp.ApplicationServices/ValidationRules/CourseRules.cs b/server/StudySharp.ApplicationServices/ValidationRules/CourseRules.cs
new file mode 100644
index 0000000..353b64c
--- /dev/null
+++ b/server/StudySharp.ApplicationServices/ValidationRules/CourseRules.cs
@@ -0,0 +1,33 @@
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.EntityFrameworkCore;
+using StudySharp.Domain.ValidationRules;
+using StudySharp.DomainServices;
+
+namespace StudySharp.ApplicationServices.ValidationRules
+{
+    public class CourseRules : ICourseRules
+    {
+        private readonly StudySharpDbContext _context;
+
+        public CourseRules(StudySharpDbContext context)
+        {
+            _context = context;
+        }
+
+        public async Task<bool> IsNameUniqueAsync(string name, int teacherId, CancellationToken cancellationToken)
+        {
+            return !await _context.Courses.AnyAsync(_ => _.Name == name && _.TeacherId == teacherId, cancellationToken);
+        }
+
+        public async Task<bool> IsCourseIdExistAsync(int id, CancellationToken cancellationToken)
+        {
+            return await _context.Courses.AnyAsync(_ => _.Id == id, cancellationToken);
+        }
+
+        public async Task<bool> IsTeacherIdExistAsync(int teacherId, CancellationToken cancellationToken)
+        {
+            return await _context.Teachers.AnyAsync(_ => _.Id == teacherId, cancellationToken);
+        }
+    }
+}
\ No newline at end of file
diff --git a/server/StudySharp.Domain/ValidationRules/ICourseRules.cs b/server/StudySharp.Domain/ValidationRules/ICourseRules.cs
new file mode 100644
index 0000000..f9bc374
--- /dev/null
+++ b/server/StudySharp.Domain/ValidationRules/ICourseRules.cs
@@ -0,0 +1,12 @@
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace StudySharp.Domain.ValidationRules
+{
+    public interface ICourseRules : IValidationRule
+    {
+        Task<bool> IsCourseIdExistAsync(int id, CancellationToken cancellationToken);
+        Task<bool> IsTeacherIdExistAsync(int teacherId, CancellationToken cancellationToken);
+        Task<bool> IsNameUniqueAsync(string name, int teacherId, CancellationToken cancellationToken);
+    }
+}
\ No newline at end of file