diff --git a/SurveyLib.Core/Class1.cs b/SurveyLib.Core/Class1.cs
deleted file mode 100644
index 41c44da..0000000
--- a/SurveyLib.Core/Class1.cs
+++ /dev/null
@@ -1,5 +0,0 @@
-namespace SurveyLib.Core;
-
-public class Class1
-{
-}
\ No newline at end of file
diff --git a/SurveyLib.Core/Models/Answer.cs b/SurveyLib.Core/Models/Answer.cs
new file mode 100644
index 0000000..d95d799
--- /dev/null
+++ b/SurveyLib.Core/Models/Answer.cs
@@ -0,0 +1,11 @@
+namespace SurveyLib.Core.Models;
+
+public class Answer
+{
+    public int CompletionId { get; set; }
+    public int QuestionId { get; set; }
+    public string AnswerText { get; set; }
+
+    public Completion Completion { get; set; }
+    public QuestionBase Question { get; set; }
+}
\ No newline at end of file
diff --git a/SurveyLib.Core/Models/Completion.cs b/SurveyLib.Core/Models/Completion.cs
new file mode 100644
index 0000000..0ba6cf3
--- /dev/null
+++ b/SurveyLib.Core/Models/Completion.cs
@@ -0,0 +1,11 @@
+namespace SurveyLib.Core.Models;
+
+public class Completion
+{
+    public int Id { get; set; }
+    public int SurveyId { get; set; }
+    public DateTime FinishedAt { get; set; }
+
+    public Survey Survey { get; set; }
+    public ICollection<Answer> Answers { get; set; }
+}
\ No newline at end of file
diff --git a/SurveyLib.Core/Models/QuestionBase.cs b/SurveyLib.Core/Models/QuestionBase.cs
new file mode 100644
index 0000000..4f2f581
--- /dev/null
+++ b/SurveyLib.Core/Models/QuestionBase.cs
@@ -0,0 +1,11 @@
+namespace SurveyLib.Core.Models;
+
+public class QuestionBase
+{
+    public int Id { get; set; }
+    public int SurveyId { get; set; }
+    public string Title { get; set; }
+
+    public Survey Survey { get; set; }
+    public ICollection<Answer> Answers { get; set; }
+}
\ No newline at end of file
diff --git a/SurveyLib.Core/Models/Survey.cs b/SurveyLib.Core/Models/Survey.cs
new file mode 100644
index 0000000..c35cdd4
--- /dev/null
+++ b/SurveyLib.Core/Models/Survey.cs
@@ -0,0 +1,11 @@
+namespace SurveyLib.Core.Models;
+
+public class Survey
+{
+    public int Id { get; set; }
+    public string Title { get; set; }
+    public string Description { get; set; }
+
+    public ICollection<QuestionBase> Questions { get; set; }
+    public ICollection<Completion> Completions { get; set; }
+}
\ No newline at end of file
diff --git a/SurveyLib.Core/Repositories/IAnswerRepository.cs b/SurveyLib.Core/Repositories/IAnswerRepository.cs
new file mode 100644
index 0000000..7766933
--- /dev/null
+++ b/SurveyLib.Core/Repositories/IAnswerRepository.cs
@@ -0,0 +1,9 @@
+using SurveyLib.Core.Models;
+
+namespace SurveyLib.Core.Repositories;
+
+public interface IAnswerRepository : IGenericRepository<Answer>
+{
+    Task<IEnumerable<Answer>> GetByAttemptIdAsync(int attemptId);
+    Task<IEnumerable<Answer>> GetByQuestionIdAsync(int questionId);
+}
\ No newline at end of file
diff --git a/SurveyLib.Core/Repositories/ICompletionRepository.cs b/SurveyLib.Core/Repositories/ICompletionRepository.cs
new file mode 100644
index 0000000..8145c1c
--- /dev/null
+++ b/SurveyLib.Core/Repositories/ICompletionRepository.cs
@@ -0,0 +1,8 @@
+using SurveyLib.Core.Models;
+
+namespace SurveyLib.Core.Repositories;
+
+public interface ICompletionRepository : IGenericRepository<Completion>
+{
+    Task<IEnumerable<Completion>> GetBySurveyIdAsync(int surveyId);
+}
\ No newline at end of file
diff --git a/SurveyLib.Core/Repositories/IGenericRepository.cs b/SurveyLib.Core/Repositories/IGenericRepository.cs
new file mode 100644
index 0000000..071416f
--- /dev/null
+++ b/SurveyLib.Core/Repositories/IGenericRepository.cs
@@ -0,0 +1,10 @@
+namespace SurveyLib.Core.Repositories;
+
+public interface IGenericRepository<T> where T : class
+{
+    Task<T>? GetByIdAsync(int id);
+    Task<IEnumerable<T>> GetAllAsync();
+    Task AddAsync(T entity);
+    Task UpdateAsync(T entity);
+    Task DeleteAsync(T entity);
+}
diff --git a/SurveyLib.Core/Repositories/IQuestionRepository.cs b/SurveyLib.Core/Repositories/IQuestionRepository.cs
new file mode 100644
index 0000000..d8ecf6c
--- /dev/null
+++ b/SurveyLib.Core/Repositories/IQuestionRepository.cs
@@ -0,0 +1,9 @@
+using SurveyLib.Core.Models;
+
+namespace SurveyLib.Core.Repositories;
+
+public interface IQuestionRepository : IGenericRepository<QuestionBase>
+{
+    Task<QuestionBase?> GetWithAnswersAsync(int questionId);
+    Task<IEnumerable<QuestionBase>> GetBySurveyIdAsync(int surveyId);
+}
\ No newline at end of file
diff --git a/SurveyLib.Core/Repositories/ISurveyRepository.cs b/SurveyLib.Core/Repositories/ISurveyRepository.cs
new file mode 100644
index 0000000..795c26d
--- /dev/null
+++ b/SurveyLib.Core/Repositories/ISurveyRepository.cs
@@ -0,0 +1,10 @@
+using SurveyLib.Core.Models;
+
+namespace SurveyLib.Core.Repositories;
+
+public interface ISurveyRepository : IGenericRepository<Survey>
+{
+    Task<Survey?> GetWithQuestionsAsync(int surveyId);
+    Task<Survey?> GetWithCompletionsAsync(int surveyId);
+    Task<Survey?> FindByTitleAsync(string title);
+}
\ No newline at end of file