diff --git a/src/Model/Collection/AbstractSet.php b/src/Model/Collection/AbstractSet.php
new file mode 100644
index 0000000..007fb1c
--- /dev/null
+++ b/src/Model/Collection/AbstractSet.php
@@ -0,0 +1,63 @@
+<?php
+/**
+ * This file is part of the Composite Utils package.
+ *
+ * (c) Emily Shepherd <emily@emilyshepherd.me>
+ *
+ * For the full copyright and license information, please view the
+ * LICENSE.md file that was distributed with this source code.
+ *
+ * @package spaark/composite-utils
+ * @author Emily Shepherd <emily@emilyshepherd.me>
+ * @license MIT
+ */
+
+namespace Spaark\CompositeUtils\Model\Collection;
+
+/**
+ * Represents an abstract collection which acts as a list of items
+ */
+abstract class AbstractSet
+    extends AbstractCollection
+    implements SetInterface
+{
+    /**
+     * {@inheritDoc}
+     */
+    public function offsetSet($offset, $value)
+    {
+        if ($offset === null)
+        {
+            $this->push($value);
+        }
+        else
+        {
+            throw new \Exception();
+        }
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function offsetUnset($index)
+    {
+        throw new \Exception();
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function offsetExists($index)
+    {
+        throw new \Exception();
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function offsetGet($index)
+    {
+        throw new \Exception();
+    }
+}
+
diff --git a/src/Model/Collection/HashSet.php b/src/Model/Collection/HashSet.php
new file mode 100644
index 0000000..6e89864
--- /dev/null
+++ b/src/Model/Collection/HashSet.php
@@ -0,0 +1,73 @@
+<?php
+/**
+ * This file is part of the Composite Utils package.
+ *
+ * (c) Emily Shepherd <emily@emilyshepherd.me>
+ *
+ * For the full copyright and license information, please view the
+ * LICENSE.md file that was distributed with this source code.
+ *
+ * @package spaark/composite-utils
+ * @author Emily Shepherd <emily@emilyshepherd.me>
+ * @license MIT
+ */
+
+namespace Spaark\CompositeUtils\Model\Collection;
+
+use ArrayIterator;
+use Spaark\CompositeUtils\Service\HashProducer;
+
+/**
+ * Represents an List stored in a PHP array
+ */
+class HashSet extends AbstractSet
+{
+    /**
+     * @var ValueType[]
+     */
+    protected $data = [];
+
+    /**
+     * {@inheritDoc}
+     */
+    public function add($item)
+    {
+        $this->data[HashProducer::getHash($item)] = $item;
+    }
+
+    /**
+     * Checks if an element exists
+     *
+     * @param ValueType The item to search for
+     * @return boolean If the item exists
+     */
+    public function contains($item) : bool
+    {
+        return isset($this->data[HashProducer::getHash($item)]);
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function remove($item)
+    {
+        unset($this->data[HashProducer::getHash($item)]);
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function getIterator()
+    {
+        return new ArrayIterator($this->data);
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function size() : int
+    {
+        return count($this->data);
+    }
+}
+
diff --git a/src/Model/Collection/SetInterface.php b/src/Model/Collection/SetInterface.php
new file mode 100644
index 0000000..c1873c9
--- /dev/null
+++ b/src/Model/Collection/SetInterface.php
@@ -0,0 +1,35 @@
+<?php
+/**
+ * This file is part of the Composite Utils package.
+ *
+ * (c) Emily Shepherd <emily@emilyshepherd.me>
+ *
+ * For the full copyright and license information, please view the
+ * LICENSE.md file that was distributed with this source code.
+ *
+ * @package spaark/composite-utils
+ * @author Emily Shepherd <emily@emilyshepherd.me>
+ * @license MIT
+ */
+
+namespace Spaark\CompositeUtils\Model\Collection;
+
+/**
+ * Represents an abstract collection which acts as a list of items
+ */
+interface SetInterface extends CollectionInterface
+{
+    /**
+     * Adds a new item to the end of the list
+     *
+     * @param ValueType $item The item to add
+     */
+    public function add($item) : bool;
+
+    /**
+     * Removes an item from the list, specified by its index
+     *
+     * @parami ValueType $item The item to remove
+     */
+    public function remove($item);
+}