diff --git a/domain-model.png b/domain-model.png
new file mode 100644
index 000000000..2955daaee
Binary files /dev/null and b/domain-model.png differ
diff --git a/src/main/java/com/booleanuk/core/Task.java b/src/main/java/com/booleanuk/core/Task.java
new file mode 100644
index 000000000..45b3ccf8c
--- /dev/null
+++ b/src/main/java/com/booleanuk/core/Task.java
@@ -0,0 +1,22 @@
+package com.booleanuk.core;
+
+public class Task {
+    private boolean completed = false;    
+    private String name;
+
+    public Task(String name) {
+        this.name = name;
+    }
+
+    void complete() {
+        completed = true;
+    }
+
+    boolean isComplete() {
+        return completed;
+    }
+
+    String getName() {
+        return name;
+    }
+}
diff --git a/src/main/java/com/booleanuk/core/TodoList.java b/src/main/java/com/booleanuk/core/TodoList.java
index 675adaf0b..04f7c77ba 100644
--- a/src/main/java/com/booleanuk/core/TodoList.java
+++ b/src/main/java/com/booleanuk/core/TodoList.java
@@ -1,5 +1,85 @@
 package com.booleanuk.core;
 
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Comparator;
+
 public class TodoList {
+    private ArrayList<Task> tasks = new ArrayList<>();
+
+    ArrayList<Task> addTask(Task t) {
+        tasks.add(t);
+        return tasks;
+    }
+
+    void completeTask(String taskName) {
+        for (Task t : tasks) {
+            if (t.getName().equals(taskName)) {
+                t.complete();
+            }
+        }
+    }
+
+    ArrayList<Task> getAll() {
+        return tasks;
+    }
+
+    ArrayList<Task> getCompleted() {
+        ArrayList<Task> completed = new ArrayList<>();
+
+        for (Task t : tasks) {
+            if (t.isComplete())
+                completed.add(t);
+        }
+
+        return completed;
+    }
+
+    ArrayList<Task> getIncompleted() {
+        ArrayList<Task> incompleted = new ArrayList<>();
+
+        for (Task t : tasks) {
+            if (!t.isComplete())
+                incompleted.add(t);
+        }
+
+        return incompleted;
+    }
+
+    ArrayList<Task> getAllAscending() {
+        Collections.sort(tasks, new Comparator<Task>() {
+            @Override
+            public int compare(Task t1, Task t2) {
+                return t1.getName().compareToIgnoreCase(t2.getName());
+            }
+        });
+        return tasks;
+    }
+
+    ArrayList<Task> getAllDescending() {
+        Collections.sort(tasks, new Comparator<Task>() {
+            @Override
+            public int compare(Task t1, Task t2) {
+                return t2.getName().compareToIgnoreCase(t1.getName());
+            }
+        });
+        return tasks;
+    }
+
+    boolean search(String taskName) {
+        for (Task t : tasks) {
+            if (t.getName().equals(taskName))
+                return true;
+        }
+        return false;
+    }
 
+    Task removeTask(String taskName) {
+        for (int i = 0; i < tasks.size(); i++) {
+            if (tasks.get(i).getName().equals(taskName)) {
+                return tasks.remove(i);
+            }
+        }
+        return null;
+    }
 }
diff --git a/src/main/java/com/booleanuk/extension/Task.java b/src/main/java/com/booleanuk/extension/Task.java
new file mode 100644
index 000000000..50d964723
--- /dev/null
+++ b/src/main/java/com/booleanuk/extension/Task.java
@@ -0,0 +1,52 @@
+package com.booleanuk.extension;
+
+import java.time.LocalDateTime;
+
+public class Task {
+    private boolean completed = false;    
+    private String name;
+    private int id = -1;
+    private LocalDateTime timeCreated = LocalDateTime.now();
+
+    public Task(String name) {
+        this.name = name;
+    }
+
+    public Task(String name, int id) {
+        this.name = name;
+        this.id = id;
+    }
+
+
+    void complete() {
+        completed = true;
+    }
+
+    boolean isComplete() {
+        return completed;
+    }
+
+    String getName() {
+        return name;
+    }
+
+    int getId() {
+        return id;
+    }
+
+    void changeName(String newName) {
+        name = newName;
+    }
+
+    void setStatus(boolean completed) {
+        this.completed = completed;
+    }
+
+    LocalDateTime getTimeCreated() {
+        return timeCreated;
+    }
+
+    void setId(int id) {
+        this.id = id;
+    }
+}
diff --git a/src/main/java/com/booleanuk/extension/TodoList.java b/src/main/java/com/booleanuk/extension/TodoList.java
new file mode 100644
index 000000000..91eb192cd
--- /dev/null
+++ b/src/main/java/com/booleanuk/extension/TodoList.java
@@ -0,0 +1,114 @@
+package com.booleanuk.extension;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Comparator;
+
+public class TodoList {
+    private ArrayList<Task> tasks = new ArrayList<>();
+    private int idCounter = 1; // gives unique ids to tasks
+
+    ArrayList<Task> addTask(Task t) {
+        t.setId(idCounter++);
+        tasks.add(t);
+        return tasks;
+    }
+
+    void completeTask(String taskName) {
+        for (Task t : tasks) {
+            if (t.getName().equals(taskName)) {
+                t.complete();
+            }
+        }
+    }
+
+    ArrayList<Task> getAll() {
+        return tasks;
+    }
+
+    ArrayList<Task> getCompleted() {
+        ArrayList<Task> completed = new ArrayList<>();
+
+        for (Task t : tasks) {
+            if (t.isComplete())
+                completed.add(t);
+        }
+
+        return completed;
+    }
+
+    ArrayList<Task> getIncompleted() {
+        ArrayList<Task> incompleted = new ArrayList<>();
+
+        for (Task t : tasks) {
+            if (!t.isComplete())
+                incompleted.add(t);
+        }
+
+        return incompleted;
+    }
+
+    ArrayList<Task> getAllAscending() {
+        ArrayList<Task> ascending = new ArrayList<>(tasks);
+        Collections.sort(ascending, new Comparator<Task>() {
+            @Override
+            public int compare(Task t1, Task t2) {
+                return t1.getName().compareToIgnoreCase(t2.getName());
+            }
+        });
+        return ascending;
+    }
+
+    ArrayList<Task> getAllDescending() {
+        ArrayList<Task> descending = getAllAscending();
+        Collections.reverse(descending);
+        return descending;
+    }
+
+    boolean search(String taskName) {
+        for (Task t : tasks) {
+            if (t.getName().equals(taskName))
+                return true;
+        }
+        return false;
+    }
+
+    Task removeTask(String taskName) {
+        for (int i = 0; i < tasks.size(); i++) {
+            if (tasks.get(i).getName().equals(taskName)) {
+                return tasks.remove(i);
+            }
+        }
+        return null;
+    }
+
+    Task getTaskId(int id) {
+        for (Task t : tasks) {
+            if (t.getId() == id)
+                return t;
+        }
+        return null;
+    }
+
+    Task changeTaskName(int id, String newName) {
+        Task t = getTaskId(id);
+
+        if (t != null) {
+            t.changeName(newName);
+            return t;
+        }
+
+        return null;
+    }
+
+    Task setTaskStatus(boolean completed, int id) {
+        Task t = getTaskId(id);
+
+        if (t != null) {
+            t.setStatus(completed);
+            return t;
+        }
+
+        return null;
+    }
+}
diff --git a/src/test/java/com/booleanuk/core/TaskTest.java b/src/test/java/com/booleanuk/core/TaskTest.java
new file mode 100644
index 000000000..dbcbc9fb6
--- /dev/null
+++ b/src/test/java/com/booleanuk/core/TaskTest.java
@@ -0,0 +1,24 @@
+package com.booleanuk.core;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class TaskTest {
+    @Test
+    void testComplete() {
+        Task task = new Task("task1");
+
+        Assertions.assertFalse(task.isComplete());
+
+        task.complete();
+
+        Assertions.assertTrue(task.isComplete());
+    }    
+
+    @Test
+    void testGetName() {
+        Task task = new Task("task1");
+
+        Assertions.assertEquals("task1", task.getName());
+    }
+}
diff --git a/src/test/java/com/booleanuk/core/TodoListTest.java b/src/test/java/com/booleanuk/core/TodoListTest.java
index 0bef779a4..168f35f96 100644
--- a/src/test/java/com/booleanuk/core/TodoListTest.java
+++ b/src/test/java/com/booleanuk/core/TodoListTest.java
@@ -1,13 +1,169 @@
 package com.booleanuk.core;
 
+import java.util.ArrayList;
+
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 
 class TodoListTest {
     @Test
-    public void exampleTest() {
-        String hello = "Hello";
-        Assertions.assertEquals("Hello", hello);
-        Assertions.assertNotEquals("Goodbye", hello);
+    void testGetAll() {
+        TodoList todoList = new TodoList();
+
+        Task task1 = new Task("task1");
+        Task task2 = new Task("task2");
+        Task task3 = new Task("task3");
+
+        todoList.addTask(task1);
+        todoList.addTask(task2);
+        todoList.addTask(task3);
+
+        ArrayList<Task> tasks = todoList.getAll();
+
+        Assertions.assertEquals(tasks.get(0), task1);
+        Assertions.assertEquals(tasks.get(1), task2);
+        Assertions.assertEquals(tasks.get(2), task3);
+    }
+
+    @Test
+    void testAddTask() {
+        TodoList todoList = new TodoList();
+
+        Task task1 = new Task("task1");
+
+        Assertions.assertEquals(task1, todoList.addTask(task1).get(0));
+    }
+
+    @Test
+    void testCompleteTask() {
+        TodoList todoList = new TodoList();
+
+        Task task1 = new Task("task1");
+        todoList.addTask(task1);
+        todoList.completeTask("task1");
+
+        Assertions.assertTrue(todoList.getAll().get(0).isComplete());
+    }
+
+    @Test
+    void testGetCompleted() {
+        TodoList todoList = new TodoList();
+
+        Task task1 = new Task("task1");
+        Task task2 = new Task("task2");
+        Task task3 = new Task("task3");
+
+        todoList.addTask(task1);
+        todoList.addTask(task2);
+        todoList.addTask(task3);
+
+        todoList.completeTask("task1");
+
+        ArrayList<Task> completed = todoList.getCompleted();
+
+        Assertions.assertEquals("task1", completed.get(0).getName());
+        Assertions.assertEquals(1, completed.size());
+    }
+
+    @Test
+    void testGetIncompleted() {
+        TodoList todoList = new TodoList();
+
+        Task task1 = new Task("task1");
+        Task task2 = new Task("task2");
+        Task task3 = new Task("task3");
+
+        todoList.addTask(task1);
+        todoList.addTask(task2);
+        todoList.addTask(task3);
+
+        todoList.completeTask("task1");
+
+        ArrayList<Task> incompleted = todoList.getIncompleted();
+
+        Assertions.assertEquals("task2", incompleted.get(0).getName());
+        Assertions.assertEquals("task3", incompleted.get(1).getName());
+        Assertions.assertEquals(2, incompleted.size());
+    }
+
+    @Test
+    void testSearch() {
+        TodoList todoList = new TodoList();
+
+        Task task1 = new Task("task1");
+        Task task2 = new Task("task2");
+        Task task3 = new Task("task3");
+
+        todoList.addTask(task1);
+        todoList.addTask(task2);
+        todoList.addTask(task3);
+
+        Assertions.assertTrue(todoList.search("task1"));
+        Assertions.assertFalse(todoList.search("task0"));
+    }
+
+    @Test
+    void testGetAllAscending() {
+        TodoList todoList = new TodoList();
+
+        Task task1 = new Task("a");
+        Task task2 = new Task("b");
+        Task task3 = new Task("c");
+
+        todoList.addTask(task1);
+        todoList.addTask(task3);
+        todoList.addTask(task2);
+
+        ArrayList<Task> tasks = todoList.getAllAscending();
+
+        Assertions.assertEquals("a", tasks.get(0).getName());
+        Assertions.assertEquals("b", tasks.get(1).getName());
+        Assertions.assertEquals("c", tasks.get(2).getName());
+    }
+
+    @Test
+    void testGetAllDescending() {
+        TodoList todoList = new TodoList();
+
+        Task task1 = new Task("a");
+        Task task2 = new Task("b");
+        Task task3 = new Task("c");
+
+        todoList.addTask(task1);
+        todoList.addTask(task2);
+        todoList.addTask(task3);
+
+        ArrayList<Task> tasks = todoList.getAllDescending();
+
+        Assertions.assertEquals("c", tasks.get(0).getName());
+        Assertions.assertEquals("b", tasks.get(1).getName());
+        Assertions.assertEquals("a", tasks.get(2).getName());
+    }
+
+    @Test
+    void testRemoveTask() {
+        TodoList todoList = new TodoList();
+
+        Task task1 = new Task("a");
+        Task task2 = new Task("b");
+        Task task3 = new Task("c");
+
+        todoList.addTask(task1);
+        todoList.addTask(task2);
+        todoList.addTask(task3);
+
+
+        Assertions.assertEquals("b", todoList.removeTask("b").getName());
+
+        ArrayList<Task> tasks = todoList.getAll();
+
+        Assertions.assertEquals(2, tasks.size());
+    }
+
+    @Test
+    void testRemoveTaskThatDoesNotExist() {
+        TodoList todoList = new TodoList();
+
+        Assertions.assertEquals(null, todoList.removeTask("task1"));
     }
-}
+}
\ No newline at end of file
diff --git a/src/test/java/com/booleanuk/extension/TaskExtensionTest.java b/src/test/java/com/booleanuk/extension/TaskExtensionTest.java
new file mode 100644
index 000000000..506352a8e
--- /dev/null
+++ b/src/test/java/com/booleanuk/extension/TaskExtensionTest.java
@@ -0,0 +1,80 @@
+package com.booleanuk.extension;
+
+import java.time.LocalDateTime;
+import java.time.temporal.ChronoUnit;
+import java.util.concurrent.TimeUnit;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class TaskExtensionTest {
+    @Test
+    void testComplete() {
+        Task task = new Task("task1");
+
+        Assertions.assertFalse(task.isComplete());
+
+        task.complete();
+
+        Assertions.assertTrue(task.isComplete());
+    }    
+
+    @Test
+    void testGetName() {
+        Task task = new Task("task1");
+
+        Assertions.assertEquals("task1", task.getName());
+    }
+
+    @Test
+    void testGetId() {
+        Task task = new Task("task1", 1);
+
+        Assertions.assertEquals(1, task.getId());
+    }
+
+    @Test
+    void testChangeName() {
+        Task task = new Task("task1");
+        task.changeName("task2");
+
+        Assertions.assertEquals("task2", task.getName());
+    }
+
+    @Test
+    void testSetStatus() {
+        Task task = new Task("task1");
+
+        task.setStatus(true);
+        Assertions.assertTrue(task.isComplete());
+
+        task.setStatus(false);
+        Assertions.assertFalse(task.isComplete());
+    }
+
+    @Test
+    void testGetTimeCreated() {
+        Task task = new Task("task1");
+        LocalDateTime time = task.getTimeCreated();
+        LocalDateTime now = LocalDateTime.now();
+
+        try {
+            TimeUnit.SECONDS.sleep(1);
+        } catch (Exception e) {
+            System.err.println(e);
+        }
+
+        Task task2 = new Task("task2");
+
+        Assertions.assertTrue(Math.abs(ChronoUnit.MILLIS.between(time, now)) < 50);
+        Assertions.assertNotEquals(time, task2.getTimeCreated());
+    }
+
+    @Test
+    void testSetId() {
+        Task task = new Task("task1");
+        
+        task.setId(777);
+        Assertions.assertEquals(777, task.getId());
+    }
+}
diff --git a/src/test/java/com/booleanuk/extension/TodoListExtensionTest.java b/src/test/java/com/booleanuk/extension/TodoListExtensionTest.java
new file mode 100644
index 000000000..c369fe99d
--- /dev/null
+++ b/src/test/java/com/booleanuk/extension/TodoListExtensionTest.java
@@ -0,0 +1,260 @@
+package com.booleanuk.extension;
+
+import java.util.ArrayList;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class TodoListExtensionTest {
+    @Test
+    void testGetAll() {
+        TodoList todoList = new TodoList();
+
+        Task task1 = new Task("task1");
+        Task task2 = new Task("task2");
+        Task task3 = new Task("task3");
+
+        todoList.addTask(task1);
+        todoList.addTask(task2);
+        todoList.addTask(task3);
+
+        ArrayList<Task> tasks = todoList.getAll();
+
+        Assertions.assertEquals(tasks.get(0), task1);
+        Assertions.assertEquals(tasks.get(1), task2);
+        Assertions.assertEquals(tasks.get(2), task3);
+    }
+
+    @Test
+    void testAddTask() {
+        TodoList todoList = new TodoList();
+
+        Task task1 = new Task("task1");
+
+        Assertions.assertEquals(task1, todoList.addTask(task1).get(0));
+    }
+
+    @Test
+    void testCompleteTask() {
+        TodoList todoList = new TodoList();
+
+        Task task1 = new Task("task1");
+        todoList.addTask(task1);
+        todoList.completeTask("task1");
+
+        Assertions.assertTrue(todoList.getAll().get(0).isComplete());
+    }
+
+    @Test
+    void testGetCompleted() {
+        TodoList todoList = new TodoList();
+
+        Task task1 = new Task("task1");
+        Task task2 = new Task("task2");
+        Task task3 = new Task("task3");
+
+        todoList.addTask(task1);
+        todoList.addTask(task2);
+        todoList.addTask(task3);
+
+        todoList.completeTask("task1");
+
+        ArrayList<Task> completed = todoList.getCompleted();
+
+        Assertions.assertEquals("task1", completed.get(0).getName());
+        Assertions.assertEquals(1, completed.size());
+    }
+
+    @Test
+    void testGetIncompleted() {
+        TodoList todoList = new TodoList();
+
+        Task task1 = new Task("task1");
+        Task task2 = new Task("task2");
+        Task task3 = new Task("task3");
+
+        todoList.addTask(task1);
+        todoList.addTask(task2);
+        todoList.addTask(task3);
+
+        todoList.completeTask("task1");
+
+        ArrayList<Task> incompleted = todoList.getIncompleted();
+
+        Assertions.assertEquals("task2", incompleted.get(0).getName());
+        Assertions.assertEquals("task3", incompleted.get(1).getName());
+        Assertions.assertEquals(2, incompleted.size());
+    }
+
+    @Test
+    void testSearch() {
+        TodoList todoList = new TodoList();
+
+        Task task1 = new Task("task1");
+        Task task2 = new Task("task2");
+        Task task3 = new Task("task3");
+
+        todoList.addTask(task1);
+        todoList.addTask(task2);
+        todoList.addTask(task3);
+
+        Assertions.assertTrue(todoList.search("task1"));
+        Assertions.assertFalse(todoList.search("task0"));
+    }
+
+    @Test
+    void testGetAllAscending() {
+        TodoList todoList = new TodoList();
+
+        Task task1 = new Task("a");
+        Task task2 = new Task("b");
+        Task task3 = new Task("c");
+
+        todoList.addTask(task1);
+        todoList.addTask(task3);
+        todoList.addTask(task2);
+
+        ArrayList<Task> tasks = todoList.getAllAscending();
+
+        Assertions.assertEquals("a", tasks.get(0).getName());
+        Assertions.assertEquals("b", tasks.get(1).getName());
+        Assertions.assertEquals("c", tasks.get(2).getName());
+    }
+
+    @Test
+    void testGetAllDescending() {
+        TodoList todoList = new TodoList();
+
+        Task task1 = new Task("a");
+        Task task2 = new Task("b");
+        Task task3 = new Task("c");
+
+        todoList.addTask(task1);
+        todoList.addTask(task2);
+        todoList.addTask(task3);
+
+        ArrayList<Task> tasks = todoList.getAllDescending();
+
+        Assertions.assertEquals("c", tasks.get(0).getName());
+        Assertions.assertEquals("b", tasks.get(1).getName());
+        Assertions.assertEquals("a", tasks.get(2).getName());
+    }
+
+    @Test
+    void testRemoveTask() {
+        TodoList todoList = new TodoList();
+
+        Task task1 = new Task("a");
+        Task task2 = new Task("b");
+        Task task3 = new Task("c");
+
+        todoList.addTask(task1);
+        todoList.addTask(task2);
+        todoList.addTask(task3);
+
+
+        Assertions.assertEquals("b", todoList.removeTask("b").getName());
+
+        ArrayList<Task> tasks = todoList.getAll();
+
+        Assertions.assertEquals(2, tasks.size());
+    }
+
+    @Test
+    void testRemoveTaskThatDoesNotExist() {
+        TodoList todoList = new TodoList();
+
+        Assertions.assertEquals(null, todoList.removeTask("task1"));
+    }
+
+    @Test
+    void testGetExistingTaskId() {
+        TodoList todoList = new TodoList();
+
+        Task task1 = new Task("a", 1);
+        Task task2 = new Task("b", 2);
+        Task task3 = new Task("c", 3);
+
+        todoList.addTask(task1);
+        todoList.addTask(task2);
+        todoList.addTask(task3);
+
+        Assertions.assertEquals("b", todoList.getTaskId(2).getName());
+    }
+
+    @Test
+    void testGetNonExistingTaskId() {
+        TodoList todoList = new TodoList();
+
+        Task task1 = new Task("a", 1);
+        Task task2 = new Task("b", 2);
+        Task task3 = new Task("c", 3);
+
+        todoList.addTask(task1);
+        todoList.addTask(task2);
+        todoList.addTask(task3);
+
+        Assertions.assertEquals(null, todoList.getTaskId(4));
+    }
+
+    @Test
+    void testChangeExistingTaskName() {
+        TodoList todoList = new TodoList();
+
+        Task task1 = new Task("a");
+        Task task2 = new Task("b");
+        Task task3 = new Task("c");
+
+        todoList.addTask(task1);
+        todoList.addTask(task2);
+        todoList.addTask(task3);
+
+        Assertions.assertEquals("d", todoList.changeTaskName(task3.getId(), "d").getName());
+    }
+
+    @Test
+    void testChangeNonExistingTaskName() {
+        TodoList todoList = new TodoList();
+
+        Task task1 = new Task("a", 1);
+        Task task2 = new Task("b", 2);
+        Task task3 = new Task("c", 3);
+
+        todoList.addTask(task1);
+        todoList.addTask(task2);
+        todoList.addTask(task3);
+
+        Assertions.assertEquals(null, todoList.changeTaskName(4, "d"));
+    }
+
+    @Test
+    void testSetExistingTaskStatus() {
+        TodoList todoList = new TodoList();
+
+        Task task1 = new Task("a");
+        Task task2 = new Task("b");
+        Task task3 = new Task("c");
+
+        todoList.addTask(task1);
+        todoList.addTask(task2);
+        todoList.addTask(task3);
+
+        Assertions.assertTrue(todoList.setTaskStatus(true, task2.getId()).isComplete());
+        Assertions.assertFalse(todoList.setTaskStatus(false, task2.getId()).isComplete());
+    }
+    @Test
+
+    void testSetNonExistingTaskStatus() {
+        TodoList todoList = new TodoList();
+
+        Task task1 = new Task("a", 1);
+        Task task2 = new Task("b", 2);
+        Task task3 = new Task("c", 3);
+
+        todoList.addTask(task1);
+        todoList.addTask(task2);
+        todoList.addTask(task3);
+
+        Assertions.assertEquals(null, todoList.setTaskStatus(true, 4));
+    }
+}