diff --git a/backend/Platform.Prerequisites.Tests/InMemoryPrerequisiteRepositoryTests.cs b/backend/Platform.Prerequisites.Tests/InMemoryPrerequisiteRepositoryTests.cs
new file mode 100644
index 0000000..3a09b92
--- /dev/null
+++ b/backend/Platform.Prerequisites.Tests/InMemoryPrerequisiteRepositoryTests.cs
@@ -0,0 +1,88 @@
+using NUnit.Framework;
+using Platform.Prerequisites.Domain;
+using Platform.Prerequisites.Infrastructure;
+
+namespace Platform.Prerequisites.Tests;
+
+[TestFixture]
+public class InMemoryPrerequisiteRepositoryTests
+{
+    private readonly Guid _labA = Guid.NewGuid();
+    private readonly Guid _labB = Guid.NewGuid();
+
+    [Test]
+    public async Task AddAsync_NewPrerequisite_IsSaved()
+    {
+        var repository = new InMemoryPrerequisiteRepository();
+
+        AddPrerequisiteResult result =
+            await repository.AddAsync(new LabPrerequisite(_labA, _labB));
+        var saved = await repository.GetForLaboratoryAsync(_labA);
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(result, Is.EqualTo(AddPrerequisiteResult.Added));
+            Assert.That(saved, Has.Count.EqualTo(1));
+        });
+    }
+
+    [Test]
+    public async Task AddAsync_Duplicate_IsRejected()
+    {
+        var repository = new InMemoryPrerequisiteRepository();
+        await repository.AddAsync(new LabPrerequisite(_labA, _labB));
+
+        AddPrerequisiteResult result =
+            await repository.AddAsync(new LabPrerequisite(_labA, _labB));
+        var saved = await repository.GetForLaboratoryAsync(_labA);
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(result, Is.EqualTo(AddPrerequisiteResult.Duplicate));
+            Assert.That(saved, Has.Count.EqualTo(1));
+        });
+    }
+
+    [Test]
+    public async Task AddAsync_Cycle_IsRejected()
+    {
+        var repository = new InMemoryPrerequisiteRepository();
+        await repository.AddAsync(new LabPrerequisite(_labA, _labB));
+
+        AddPrerequisiteResult result =
+            await repository.AddAsync(new LabPrerequisite(_labB, _labA));
+        var saved = await repository.GetForLaboratoryAsync(_labB);
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(result, Is.EqualTo(AddPrerequisiteResult.WouldCreateCycle));
+            Assert.That(saved, Is.Empty);
+        });
+    }
+
+    [Test]
+    public async Task RemoveAsync_ExistingPrerequisite_ReturnsTrue()
+    {
+        var repository = new InMemoryPrerequisiteRepository();
+        await repository.AddAsync(new LabPrerequisite(_labA, _labB));
+
+        bool removed = await repository.RemoveAsync(new LabPrerequisite(_labA, _labB));
+        var saved = await repository.GetForLaboratoryAsync(_labA);
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(removed, Is.True);
+            Assert.That(saved, Is.Empty);
+        });
+    }
+
+    [Test]
+    public async Task RemoveAsync_MissingPrerequisite_ReturnsFalse()
+    {
+        var repository = new InMemoryPrerequisiteRepository();
+
+        bool removed = await repository.RemoveAsync(new LabPrerequisite(_labA, _labB));
+
+        Assert.That(removed, Is.False);
+    }
+}
\ No newline at end of file
diff --git a/backend/Platform.Prerequisites.Tests/LabPrerequisiteTests.cs b/backend/Platform.Prerequisites.Tests/LabPrerequisiteTests.cs
new file mode 100644
index 0000000..e455c82
--- /dev/null
+++ b/backend/Platform.Prerequisites.Tests/LabPrerequisiteTests.cs
@@ -0,0 +1,39 @@
+using NUnit.Framework;
+using Platform.Prerequisites.Domain;
+
+namespace Platform.Prerequisites.Tests;
+
+[TestFixture]
+public class LabPrerequisiteTests
+{
+    [Test]
+    public void Constructor_ValidLaboratories_SavesBothIds()
+    {
+        Guid laboratoryId = Guid.NewGuid();
+        Guid requiredId = Guid.NewGuid();
+
+        var prerequisite = new LabPrerequisite(laboratoryId, requiredId);
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(prerequisite.LaboratoryId, Is.EqualTo(laboratoryId));
+            Assert.That(prerequisite.RequiredLaboratoryId, Is.EqualTo(requiredId));
+        });
+    }
+
+    [Test]
+    public void Constructor_SameLaboratory_IsRejected()
+    {
+        Guid laboratoryId = Guid.NewGuid();
+
+        Assert.Throws<ArgumentException>(
+            () => new LabPrerequisite(laboratoryId, laboratoryId));
+    }
+
+    [Test]
+    public void Constructor_EmptyId_IsRejected()
+    {
+        Assert.Throws<ArgumentException>(
+            () => new LabPrerequisite(Guid.Empty, Guid.NewGuid()));
+    }
+}
\ No newline at end of file
diff --git a/backend/Platform.Prerequisites.Tests/Platform.Prerequisites.Tests.csproj b/backend/Platform.Prerequisites.Tests/Platform.Prerequisites.Tests.csproj
new file mode 100644
index 0000000..b0d927d
--- /dev/null
+++ b/backend/Platform.Prerequisites.Tests/Platform.Prerequisites.Tests.csproj
@@ -0,0 +1,27 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <LangVersion>latest</LangVersion>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="coverlet.collector" Version="6.0.4" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.14.0" />
+    <PackageReference Include="NUnit" Version="4.3.2" />
+    <PackageReference Include="NUnit.Analyzers" Version="4.7.0" />
+    <PackageReference Include="NUnit3TestAdapter" Version="5.0.0" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <Using Include="NUnit.Framework" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Platform.Prerequisites\Platform.Prerequisites.csproj" />
+  </ItemGroup>
+
+</Project>
diff --git a/backend/Platform.Prerequisites.Tests/PrerequisiteRulesTests.cs b/backend/Platform.Prerequisites.Tests/PrerequisiteRulesTests.cs
new file mode 100644
index 0000000..950271d
--- /dev/null
+++ b/backend/Platform.Prerequisites.Tests/PrerequisiteRulesTests.cs
@@ -0,0 +1,106 @@
+using NUnit.Framework;
+using Platform.Prerequisites.Domain;
+
+namespace Platform.Prerequisites.Tests;
+
+[TestFixture]
+public class PrerequisiteRulesTests
+{
+    [Test]
+    public void IsDuplicate_SamePairExists_ReturnsTrue()
+    {
+        Guid labA = Guid.NewGuid();
+        Guid labB = Guid.NewGuid();
+        var existing = new[] { new LabPrerequisite(labA, labB) };
+
+        bool result = PrerequisiteRules.IsDuplicate(
+            existing,
+            new LabPrerequisite(labA, labB));
+
+        Assert.That(result, Is.True);
+    }
+
+    [Test]
+    public void IsDuplicate_DifferentPair_ReturnsFalse()
+    {
+        Guid labA = Guid.NewGuid();
+        Guid labB = Guid.NewGuid();
+        Guid labC = Guid.NewGuid();
+        var existing = new[] { new LabPrerequisite(labA, labB) };
+
+        bool result = PrerequisiteRules.IsDuplicate(
+            existing,
+            new LabPrerequisite(labA, labC));
+
+        Assert.That(result, Is.False);
+    }
+
+    [Test]
+    public void WouldCreateCycle_TwoLaboratories_ReturnsTrue()
+    {
+        Guid labA = Guid.NewGuid();
+        Guid labB = Guid.NewGuid();
+        var existing = new[] { new LabPrerequisite(labA, labB) };
+
+        bool result = PrerequisiteRules.WouldCreateCycle(
+            existing,
+            new LabPrerequisite(labB, labA));
+
+        Assert.That(result, Is.True);
+    }
+
+    [Test]
+    public void WouldCreateCycle_ThreeLaboratories_ReturnsTrue()
+    {
+        Guid labA = Guid.NewGuid();
+        Guid labB = Guid.NewGuid();
+        Guid labC = Guid.NewGuid();
+        var existing = new[]
+        {
+            new LabPrerequisite(labA, labB),
+            new LabPrerequisite(labB, labC)
+        };
+
+        bool result = PrerequisiteRules.WouldCreateCycle(
+            existing,
+            new LabPrerequisite(labC, labA));
+
+        Assert.That(result, Is.True);
+    }
+
+    [Test]
+    public void WouldCreateCycle_NormalChain_ReturnsFalse()
+    {
+        Guid labA = Guid.NewGuid();
+        Guid labB = Guid.NewGuid();
+        Guid labC = Guid.NewGuid();
+        var existing = new[] { new LabPrerequisite(labA, labB) };
+
+        bool result = PrerequisiteRules.WouldCreateCycle(
+            existing,
+            new LabPrerequisite(labB, labC));
+
+        Assert.That(result, Is.False);
+    }
+
+    [Test]
+    public void WouldCreateCycle_SharedPrerequisite_ReturnsFalse()
+    {
+        Guid labA = Guid.NewGuid();
+        Guid labB = Guid.NewGuid();
+        Guid labC = Guid.NewGuid();
+        Guid labD = Guid.NewGuid();
+        var existing = new[]
+        {
+            new LabPrerequisite(labA, labB),
+            new LabPrerequisite(labA, labC),
+            new LabPrerequisite(labB, labD)
+        };
+
+        bool result = PrerequisiteRules.WouldCreateCycle(
+            existing,
+            new LabPrerequisite(labC, labD));
+
+        Assert.That(result, Is.False);
+    }
+}
diff --git a/backend/Platform.Prerequisites.Tests/StubCompletedLaboratoriesTests.cs b/backend/Platform.Prerequisites.Tests/StubCompletedLaboratoriesTests.cs
new file mode 100644
index 0000000..2aa9697
--- /dev/null
+++ b/backend/Platform.Prerequisites.Tests/StubCompletedLaboratoriesTests.cs
@@ -0,0 +1,32 @@
+using NUnit.Framework;
+using Platform.Prerequisites.Infrastructure;
+
+namespace Platform.Prerequisites.Tests;
+
+[TestFixture]
+public class StubCompletedLaboratoriesTests
+{
+    [Test]
+    public async Task GetCompletedAsync_ReturnsMarkedLaboratory()
+    {
+        var stub = new StubCompletedLaboratories();
+        Guid studentId = Guid.NewGuid();
+        Guid laboratoryId = Guid.NewGuid();
+
+        stub.MarkCompleted(studentId, laboratoryId);
+        IReadOnlySet<Guid> completed = await stub.GetCompletedAsync(studentId);
+
+        Assert.That(completed, Does.Contain(laboratoryId));
+    }
+
+    [Test]
+    public async Task GetCompletedAsync_OtherStudent_ReturnsEmpty()
+    {
+        var stub = new StubCompletedLaboratories();
+        stub.MarkCompleted(Guid.NewGuid(), Guid.NewGuid());
+
+        IReadOnlySet<Guid> completed = await stub.GetCompletedAsync(Guid.NewGuid());
+
+        Assert.That(completed, Is.Empty);
+    }
+}
\ No newline at end of file
diff --git a/backend/Platform.Prerequisites/Contracts/ICompletedLaboratories.cs b/backend/Platform.Prerequisites/Contracts/ICompletedLaboratories.cs
new file mode 100644
index 0000000..6782f01
--- /dev/null
+++ b/backend/Platform.Prerequisites/Contracts/ICompletedLaboratories.cs
@@ -0,0 +1,8 @@
+namespace Platform.Prerequisites.Contracts;
+
+public interface ICompletedLaboratories
+{
+    Task<IReadOnlySet<Guid>> GetCompletedAsync(
+        Guid studentId,
+        CancellationToken cancellationToken = default);
+}
\ No newline at end of file
diff --git a/backend/Platform.Prerequisites/Contracts/IPrerequisiteRepository.cs b/backend/Platform.Prerequisites/Contracts/IPrerequisiteRepository.cs
new file mode 100644
index 0000000..32a145f
--- /dev/null
+++ b/backend/Platform.Prerequisites/Contracts/IPrerequisiteRepository.cs
@@ -0,0 +1,18 @@
+using Platform.Prerequisites.Domain;
+
+namespace Platform.Prerequisites.Contracts;
+
+public interface IPrerequisiteRepository
+{
+    Task<AddPrerequisiteResult> AddAsync(
+        LabPrerequisite prerequisite,
+        CancellationToken cancellationToken = default);
+
+    Task<bool> RemoveAsync(
+        LabPrerequisite prerequisite,
+        CancellationToken cancellationToken = default);
+
+    Task<IReadOnlyList<LabPrerequisite>> GetForLaboratoryAsync(
+        Guid laboratoryId,
+        CancellationToken cancellationToken = default);
+}
\ No newline at end of file
diff --git a/backend/Platform.Prerequisites/Domain/AddPrerequisiteResult.cs b/backend/Platform.Prerequisites/Domain/AddPrerequisiteResult.cs
new file mode 100644
index 0000000..791ac6e
--- /dev/null
+++ b/backend/Platform.Prerequisites/Domain/AddPrerequisiteResult.cs
@@ -0,0 +1,8 @@
+namespace Platform.Prerequisites.Domain;
+
+public enum AddPrerequisiteResult
+{
+    Added,
+    Duplicate,
+    WouldCreateCycle
+}
\ No newline at end of file
diff --git a/backend/Platform.Prerequisites/Domain/LabPrerequisite.cs b/backend/Platform.Prerequisites/Domain/LabPrerequisite.cs
new file mode 100644
index 0000000..265f9e6
--- /dev/null
+++ b/backend/Platform.Prerequisites/Domain/LabPrerequisite.cs
@@ -0,0 +1,23 @@
+namespace Platform.Prerequisites.Domain;
+
+public sealed class LabPrerequisite
+{
+    public Guid LaboratoryId { get; }
+    public Guid RequiredLaboratoryId { get; }
+
+    public LabPrerequisite(Guid laboratoryId, Guid requiredLaboratoryId)
+    {
+        if (laboratoryId == Guid.Empty || requiredLaboratoryId == Guid.Empty)
+        {
+            throw new ArgumentException("ID laboratorije ne sme biti prazan.");
+        }
+
+        if (laboratoryId == requiredLaboratoryId)
+        {
+            throw new ArgumentException("Laboratorija ne može biti sopstveni preduslov.");
+        }
+
+        LaboratoryId = laboratoryId;
+        RequiredLaboratoryId = requiredLaboratoryId;
+    }
+}
\ No newline at end of file
diff --git a/backend/Platform.Prerequisites/Domain/PrerequisiteRules.cs b/backend/Platform.Prerequisites/Domain/PrerequisiteRules.cs
new file mode 100644
index 0000000..806228c
--- /dev/null
+++ b/backend/Platform.Prerequisites/Domain/PrerequisiteRules.cs
@@ -0,0 +1,47 @@
+namespace Platform.Prerequisites.Domain;
+
+public static class PrerequisiteRules
+{
+    public static bool IsDuplicate(
+        IEnumerable<LabPrerequisite> existing,
+        LabPrerequisite candidate)
+    {
+        return existing.Any(prerequisite =>
+            prerequisite.LaboratoryId == candidate.LaboratoryId &&
+            prerequisite.RequiredLaboratoryId == candidate.RequiredLaboratoryId);
+    }
+
+    public static bool WouldCreateCycle(
+        IReadOnlyCollection<LabPrerequisite> existing,
+        LabPrerequisite candidate)
+    {
+        var visited = new HashSet<Guid>();
+        var toVisit = new Stack<Guid>();
+        toVisit.Push(candidate.RequiredLaboratoryId);
+
+        while (toVisit.Count > 0)
+        {
+            Guid current = toVisit.Pop();
+
+            if (current == candidate.LaboratoryId)
+            {
+                return true;
+            }
+
+            if (!visited.Add(current))
+            {
+                continue;
+            }
+
+            foreach (LabPrerequisite prerequisite in existing)
+            {
+                if (prerequisite.LaboratoryId == current)
+                {
+                    toVisit.Push(prerequisite.RequiredLaboratoryId);
+                }
+            }
+        }
+
+        return false;
+    }
+}
\ No newline at end of file
diff --git a/backend/Platform.Prerequisites/Infrastructure/InMemoryPrerequisiteRepository.cs b/backend/Platform.Prerequisites/Infrastructure/InMemoryPrerequisiteRepository.cs
new file mode 100644
index 0000000..0b977a4
--- /dev/null
+++ b/backend/Platform.Prerequisites/Infrastructure/InMemoryPrerequisiteRepository.cs
@@ -0,0 +1,59 @@
+using Platform.Prerequisites.Contracts;
+using Platform.Prerequisites.Domain;
+
+namespace Platform.Prerequisites.Infrastructure;
+
+public sealed class InMemoryPrerequisiteRepository : IPrerequisiteRepository
+{
+    private readonly List<LabPrerequisite> _prerequisites = new();
+    private readonly object _lock = new();
+
+    public Task<AddPrerequisiteResult> AddAsync(
+        LabPrerequisite prerequisite,
+        CancellationToken cancellationToken = default)
+    {
+        lock (_lock)
+        {
+            if (PrerequisiteRules.IsDuplicate(_prerequisites, prerequisite))
+            {
+                return Task.FromResult(AddPrerequisiteResult.Duplicate);
+            }
+
+            if (PrerequisiteRules.WouldCreateCycle(_prerequisites, prerequisite))
+            {
+                return Task.FromResult(AddPrerequisiteResult.WouldCreateCycle);
+            }
+
+            _prerequisites.Add(prerequisite);
+            return Task.FromResult(AddPrerequisiteResult.Added);
+        }
+    }
+
+    public Task<bool> RemoveAsync(
+        LabPrerequisite prerequisite,
+        CancellationToken cancellationToken = default)
+    {
+        lock (_lock)
+        {
+            int removed = _prerequisites.RemoveAll(item =>
+                item.LaboratoryId == prerequisite.LaboratoryId &&
+                item.RequiredLaboratoryId == prerequisite.RequiredLaboratoryId);
+
+            return Task.FromResult(removed > 0);
+        }
+    }
+
+    public Task<IReadOnlyList<LabPrerequisite>> GetForLaboratoryAsync(
+        Guid laboratoryId,
+        CancellationToken cancellationToken = default)
+    {
+        lock (_lock)
+        {
+            IReadOnlyList<LabPrerequisite> result = _prerequisites
+                .Where(item => item.LaboratoryId == laboratoryId)
+                .ToList();
+
+            return Task.FromResult(result);
+        }
+    }
+}
\ No newline at end of file
diff --git a/backend/Platform.Prerequisites/Infrastructure/StubCompletedLaboratories.cs b/backend/Platform.Prerequisites/Infrastructure/StubCompletedLaboratories.cs
new file mode 100644
index 0000000..b7875bb
--- /dev/null
+++ b/backend/Platform.Prerequisites/Infrastructure/StubCompletedLaboratories.cs
@@ -0,0 +1,30 @@
+using Platform.Prerequisites.Contracts;
+
+namespace Platform.Prerequisites.Infrastructure;
+
+public sealed class StubCompletedLaboratories : ICompletedLaboratories
+{
+    private readonly Dictionary<Guid, HashSet<Guid>> _completed = new();
+
+    public void MarkCompleted(Guid studentId, Guid laboratoryId)
+    {
+        if (!_completed.TryGetValue(studentId, out HashSet<Guid>? laboratories))
+        {
+            laboratories = new HashSet<Guid>();
+            _completed[studentId] = laboratories;
+        }
+
+        laboratories.Add(laboratoryId);
+    }
+
+    public Task<IReadOnlySet<Guid>> GetCompletedAsync(
+        Guid studentId,
+        CancellationToken cancellationToken = default)
+    {
+        IReadOnlySet<Guid> result = _completed.TryGetValue(studentId, out HashSet<Guid>? laboratories)
+            ? new HashSet<Guid>(laboratories)
+            : new HashSet<Guid>();
+
+        return Task.FromResult(result);
+    }
+}
\ No newline at end of file
diff --git a/backend/Platform.Prerequisites/Platform.Prerequisites.csproj b/backend/Platform.Prerequisites/Platform.Prerequisites.csproj
new file mode 100644
index 0000000..b760144
--- /dev/null
+++ b/backend/Platform.Prerequisites/Platform.Prerequisites.csproj
@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>
diff --git a/backend/SecurityLab.slnx b/backend/SecurityLab.slnx
index c8a3250..7194f0d 100644
--- a/backend/SecurityLab.slnx
+++ b/backend/SecurityLab.slnx
@@ -3,5 +3,7 @@
   <Project Path="Platform.Api/Platform.Api.csproj" />
   <Project Path="Platform.Audit/Platform.Audit.csproj" />
   <Project Path="Platform.Audit.Tests/Platform.Audit.Tests.csproj" />
+  <Project Path="Platform.Prerequisites.Tests/Platform.Prerequisites.Tests.csproj" />
+  <Project Path="Platform.Prerequisites/Platform.Prerequisites.csproj" />
   <Project Path="Platform.Tests/Platform.Tests.csproj" />
 </Solution>