diff --git a/core/lib/Drupal/Core/Entity/EntityManager.php b/core/lib/Drupal/Core/Entity/EntityManager.php
index f552c54..e7a9992 100644
--- a/core/lib/Drupal/Core/Entity/EntityManager.php
+++ b/core/lib/Drupal/Core/Entity/EntityManager.php
@@ -494,15 +494,17 @@ public function getFieldDefinitions($entity_type, $bundle = NULL) {
         // Enforce field definitions to be objects.
         foreach ($this->entityFieldInfo[$entity_type]['definitions'] as $field_name => &$definition) {
           if (is_array($definition)) {
-            $definition = FieldDefinition::createFromOldStyleDefinition($definition)
-              ->setFieldName($field_name);
+            $definition = FieldDefinition::createFromOldStyleDefinition($definition);
           }
+          // Make sure the field name is properly set.
+          $definition->setFieldName($field_name);
         }
         foreach ($this->entityFieldInfo[$entity_type]['optional'] as $field_name => &$definition) {
           if (is_array($definition)) {
-            $definition = FieldDefinition::createFromOldStyleDefinition($definition)
-              ->setFieldName($field_name);
+            $definition = FieldDefinition::createFromOldStyleDefinition($definition);
           }
+          // Make sure the field name is properly set.
+          $definition->setFieldName($field_name);
         }
         $this->cache->set($cid, $this->entityFieldInfo[$entity_type], CacheBackendInterface::CACHE_PERMANENT, array('entity_info' => TRUE, 'entity_field_info' => TRUE));
       }
diff --git a/core/lib/Drupal/Core/Entity/Field/FieldDefinition.php b/core/lib/Drupal/Core/Entity/Field/FieldDefinition.php
index 226a9ca..e46bc69 100644
--- a/core/lib/Drupal/Core/Entity/Field/FieldDefinition.php
+++ b/core/lib/Drupal/Core/Entity/Field/FieldDefinition.php
@@ -17,6 +17,25 @@
 class FieldDefinition extends ListDefinition implements FieldDefinitionInterface, \ArrayAccess {
 
   /**
+   * Creates a new entity field definition.
+   *
+   * @return \Drupal\Core\Entity\Field\FieldDefinition
+   */
+  public static function create() {
+    $class = get_called_class();
+    return new $class();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function __construct(array $definition = array()) {
+    parent::__construct($definition);
+    // Set a default list type to use.
+    $this->setDataType('entity_field');
+  }
+
+  /**
    * {@inheritdoc}
    */
   public function getFieldName() {
@@ -42,9 +61,18 @@ public function setFieldName($name) {
    * {@inheritdoc}
    */
   public function getFieldType() {
-    // Cut of the leading field_item: prefix from 'field_item:FIELD_TYPE'.
-    $parts = explode(':', $this->getItemDefinition()->getDataType());
-    return $parts[1];
+    // We have to support 'field_item:FIELD_TYPE' data types as well as
+    // 'FIELD_TYPE_field' for field types that are not yet implemented as field
+    // type plugin.
+    $data_type = $this->getItemDefinition()->getDataType();
+    if (strpos($data_type, ':') !== FALSE) {
+      // Cut of the leading field_item: prefix from 'field_item:FIELD_TYPE'.
+      $parts = explode(':', $data_type);
+      return $parts[1];
+    }
+    else {
+      return str_replace('_field', '', $data_type);
+    }
   }
 
   /**
@@ -57,7 +85,14 @@ public function getFieldType() {
    *   The object itself for chaining.
    */
   public function setFieldType($type) {
-    $this->getItemDefinition()->setDataType('field_item:' . $type);
+    // Determine the right data type to use.
+    if (\Drupal::typedData()->getDefinition('field_item:' . $type)) {
+      $this->getItemDefinition()->setDataType('field_item:' . $type);
+    }
+    else {
+      // Data type has not been converted to a field type plugin yet.
+      $this->getItemDefinition()->setDataType($type . '_field');
+    }
     return $this;
   }
 
@@ -78,7 +113,8 @@ public function getFieldSettings() {
    *   The object itself for chaining.
    */
   public function setFieldSettings(array $settings) {
-    return $this->getItemDefinition()->setSettings($settings);
+    $this->getItemDefinition()->setSettings($settings);
+    return $this;
   }
 
   /**
@@ -269,7 +305,9 @@ public static function createFromOldStyleDefinition(array $definition) {
       }
     }
 
-    // Take care of the item definition.
+    // Take care of the item definition now. 'required' applies to the list
+    // definition.
+    unset($definition['required']);
     $item_definition = new DataDefinition($definition);
     if (isset($definition['settings'])) {
       $item_definition->setSettings($definition['settings']);
@@ -302,8 +340,10 @@ public function &offsetGet($offset) {
   public function offsetSet($offset, $value) {
     if ($offset == 'type') {
       // What previously was "type" is now the type of the list item.
-      $this->itemDefinition['type'] = $value;
+      $this->itemDefinition->setDataType($value);
+    }
+    else {
+      $this->definition[$offset] = $value;
     }
-    $this->definition[$offset] = $value;
   }
 }
diff --git a/core/lib/Drupal/Core/Entity/Field/FieldItemList.php b/core/lib/Drupal/Core/Entity/Field/FieldItemList.php
deleted file mode 100644
index a2b308c..0000000
--- a/core/lib/Drupal/Core/Entity/Field/FieldItemList.php
+++ /dev/null
@@ -1,298 +0,0 @@
-<?php
-
-/**
- * @file
- * Contains \Drupal\Core\Entity\Field\FieldItemList.
- */
-
-namespace Drupal\Core\Entity\Field;
-
-use Drupal\Core\Entity\Field\FieldItemListInterface;
-use Drupal\Core\Session\AccountInterface;
-use Drupal\Core\TypedData\TypedDataInterface;
-use Drupal\Core\TypedData\Plugin\DataType\ItemList;
-use Drupal\Core\Language\Language;
-
-/**
- * Represents an entity field; that is, a list of field item objects.
- *
- * An entity field is a list of field items, which contain only primitive
- * properties or entity references. Note that even single-valued entity
- * fields are represented as list of items, however for easy access to the
- * contained item the entity field delegates __get() and __set() calls
- * directly to the first item.
- *
- * Supported settings (below the definition's 'settings' key) are:
- * - default_value: (optional) If set, the default value to apply to the field.
- */
-class FieldItemList extends ItemList implements FieldItemListInterface {
-
-  /**
-   * Numerically indexed array of field items, implementing the
-   * FieldItemInterface.
-   *
-   * @var array
-   */
-  protected $list = array();
-
-  /**
-   * The langcode of the field values held in the object.
-   *
-   * @var string
-   */
-  protected $langcode = Language::LANGCODE_DEFAULT;
-
-  /**
-   * Overrides TypedData::__construct().
-   */
-  public function __construct($definition, $name = NULL, TypedDataInterface $parent = NULL) {
-    parent::__construct($definition, $name, $parent);
-    $this->definition['field_name'] = $name;
-    // Always initialize one empty item as most times a value for at least one
-    // item will be present. That way prototypes created by
-    // \Drupal\Core\TypedData\TypedDataManager::getPropertyInstance() will
-    // already have this field item ready for use after cloning.
-    $this->list[0] = $this->createItem(0);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getEntity() {
-    return $this->getParent();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setLangcode($langcode) {
-    $this->langcode = $langcode;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getLangcode() {
-    return $this->langcode;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getFieldDefinition() {
-    return $this->definition;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function filterEmptyValues() {
-    if (isset($this->list)) {
-      $this->list = array_values(array_filter($this->list, function($item) {
-        return !$item->isEmpty();
-      }));
-    }
-  }
-
-  /**
-   * {@inheritdoc}
-   * @todo Revisit the need when all entity types are converted to NG entities.
-   */
-  public function getValue($include_computed = FALSE) {
-    if (isset($this->list)) {
-      $values = array();
-      foreach ($this->list as $delta => $item) {
-        $values[$delta] = $item->getValue($include_computed);
-      }
-      return $values;
-    }
-  }
-
-  /**
-   * Overrides \Drupal\Core\TypedData\Plugin\DataType\ItemList::setValue().
-   */
-  public function setValue($values, $notify = TRUE) {
-    if (!isset($values) || $values === array()) {
-      $this->list = $values;
-    }
-    else {
-      // Support passing in only the value of the first item.
-      if (!is_array($values) || !is_numeric(current(array_keys($values)))) {
-        $values = array(0 => $values);
-      }
-
-      // Clear the values of properties for which no value has been passed.
-      if (isset($this->list)) {
-        $this->list = array_intersect_key($this->list, $values);
-      }
-
-      // Set the values.
-      foreach ($values as $delta => $value) {
-        if (!is_numeric($delta)) {
-          throw new \InvalidArgumentException('Unable to set a value with a non-numeric delta in a list.');
-        }
-        elseif (!isset($this->list[$delta])) {
-          $this->list[$delta] = $this->createItem($delta, $value);
-        }
-        else {
-          $this->list[$delta]->setValue($value, FALSE);
-        }
-      }
-    }
-    // Notify the parent of any changes.
-    if ($notify && isset($this->parent)) {
-      $this->parent->onChange($this->name);
-    }
-  }
-
-  /**
-   * Implements \Drupal\Core\Entity\Field\FieldItemListInterface::getPropertyDefinition().
-   */
-  public function getPropertyDefinition($name) {
-    return $this->offsetGet(0)->getPropertyDefinition($name);
-  }
-
-  /**
-   * Implements \Drupal\Core\Entity\Field\FieldItemListInterface::getPropertyDefinitions().
-   */
-  public function getPropertyDefinitions() {
-    return $this->offsetGet(0)->getPropertyDefinitions();
-  }
-
-  /**
-   * Implements \Drupal\Core\Entity\Field\FieldItemListInterface::__get().
-   */
-  public function __get($property_name) {
-    return $this->offsetGet(0)->__get($property_name);
-  }
-
-  /**
-   * Implements \Drupal\Core\Entity\Field\FieldItemListInterface::get().
-   */
-  public function get($property_name) {
-    return $this->offsetGet(0)->get($property_name);
-  }
-
-  /**
-   * Implements \Drupal\Core\Entity\Field\FieldItemListInterface::__set().
-   */
-  public function __set($property_name, $value) {
-    $this->offsetGet(0)->__set($property_name, $value);
-  }
-
-  /**
-   * Implements \Drupal\Core\Entity\Field\FieldItemListInterface::__isset().
-   */
-  public function __isset($property_name) {
-    return $this->offsetGet(0)->__isset($property_name);
-  }
-
-  /**
-   * Implements \Drupal\Core\Entity\Field\FieldItemListInterface::__unset().
-   */
-  public function __unset($property_name) {
-    return $this->offsetGet(0)->__unset($property_name);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function access($operation = 'view', AccountInterface $account = NULL) {
-    $access_controller = \Drupal::entityManager()->getAccessController($this->getParent()->entityType());
-    return $access_controller->fieldAccess($operation, $this->getFieldDefinition(), $account, $this);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function defaultAccess($operation = 'view', AccountInterface $account = NULL) {
-    // Grant access per default.
-    return TRUE;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function applyDefaultValue($notify = TRUE) {
-    $value = $this->getFieldDefinition()->getFieldDefaultValue($this->getEntity());
-
-    // NULL or array() mean "no default value", but  0, '0' and the empty string
-    // are valid default values.
-    if (!isset($value) || (is_array($value) && empty($value))) {
-      // Create one field item and apply defaults.
-      $this->offsetGet(0)->applyDefaultValue(FALSE);
-    }
-    else {
-      $this->setValue($value, $notify);
-    }
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getConstraints() {
-    // Constraints usually apply to the field item, but required does make
-    // sense on the field only. So we special-case it to apply to the field for
-    // now.
-    // @todo: Separate list and list item definitions to separate constraints.
-    $constraints = array();
-    if (!empty($this->definition['required'])) {
-      $constraints[] = \Drupal::typedData()->getValidationConstraintManager()->create('NotNull', array());
-    }
-    return $constraints;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function preSave() {
-    // Filter out empty items.
-    $this->filterEmptyValues();
-
-    $this->delegateMethod('presave');
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function insert() {
-    $this->delegateMethod('insert');
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function update() {
-    $this->delegateMethod('update');
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function delete() {
-    $this->delegateMethod('delete');
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function deleteRevision() {
-    $this->delegateMethod('deleteRevision');
-  }
-
-  /**
-   * Calls a method on each FieldItem.
-   *
-   * @param string $method
-   *   The name of the method.
-   */
-  protected function delegateMethod($method) {
-    if (isset($this->list)) {
-      foreach ($this->list as $item) {
-        $item->{$method}();
-      }
-    }
-  }
-
-}
diff --git a/core/lib/Drupal/Core/Entity/Plugin/DataType/BooleanItem.php b/core/lib/Drupal/Core/Entity/Plugin/DataType/BooleanItem.php
index 31e3ec8..d1357be 100644
--- a/core/lib/Drupal/Core/Entity/Plugin/DataType/BooleanItem.php
+++ b/core/lib/Drupal/Core/Entity/Plugin/DataType/BooleanItem.php
@@ -18,7 +18,7 @@
  *   id = "boolean_field",
  *   label = @Translation("Boolean field item"),
  *   description = @Translation("An entity field containing a boolean value."),
- *   list_class = "\Drupal\Core\Entity\Field\FieldItemList"
+ *   list_class = "\Drupal\Core\Entity\Plugin\DataType\FieldItemList"
  * )
  */
 class BooleanItem extends FieldItemBase {
diff --git a/core/lib/Drupal/Core/Entity/Plugin/DataType/DateItem.php b/core/lib/Drupal/Core/Entity/Plugin/DataType/DateItem.php
index e6f462f..a23233e 100644
--- a/core/lib/Drupal/Core/Entity/Plugin/DataType/DateItem.php
+++ b/core/lib/Drupal/Core/Entity/Plugin/DataType/DateItem.php
@@ -18,7 +18,7 @@
  *   id = "date_field",
  *   label = @Translation("Date field item"),
  *   description = @Translation("An entity field containing a date value."),
- *   list_class = "\Drupal\Core\Entity\Field\FieldItemList"
+ *   list_class = "\Drupal\Core\Entity\Plugin\DataType\FieldItemList"
  * )
  */
 class DateItem extends FieldItemBase {
diff --git a/core/lib/Drupal/Core/Entity/Plugin/DataType/EmailItem.php b/core/lib/Drupal/Core/Entity/Plugin/DataType/EmailItem.php
index 6d1dba6..d736529 100644
--- a/core/lib/Drupal/Core/Entity/Plugin/DataType/EmailItem.php
+++ b/core/lib/Drupal/Core/Entity/Plugin/DataType/EmailItem.php
@@ -19,7 +19,7 @@
  *   id = "email_field",
  *   label = @Translation("E-mail field item"),
  *   description = @Translation("An entity field containing an e-mail value."),
- *   list_class = "\Drupal\Core\Entity\Field\FieldItemList"
+ *   list_class = "\Drupal\Core\Entity\Plugin\DataType\FieldItemList"
  * )
  */
 class EmailItem extends LegacyConfigFieldItem {
diff --git a/core/lib/Drupal/Core/Entity/Plugin/DataType/EntityReferenceItem.php b/core/lib/Drupal/Core/Entity/Plugin/DataType/EntityReferenceItem.php
index 5654747..e8b2980 100644
--- a/core/lib/Drupal/Core/Entity/Plugin/DataType/EntityReferenceItem.php
+++ b/core/lib/Drupal/Core/Entity/Plugin/DataType/EntityReferenceItem.php
@@ -25,7 +25,7 @@
  *   id = "entity_reference_field",
  *   label = @Translation("Entity reference field item"),
  *   description = @Translation("An entity field containing an entity reference."),
- *   list_class = "\Drupal\Core\Entity\Field\FieldItemList",
+ *   list_class = "\Drupal\Core\Entity\Plugin\DataType\FieldItemList",
  *   constraints = {"ValidReference" = TRUE}
  * )
  */
diff --git a/core/lib/Drupal/Core/Entity/Plugin/DataType/FieldItem.php b/core/lib/Drupal/Core/Entity/Plugin/DataType/FieldItem.php
index b630fc7..c338151 100644
--- a/core/lib/Drupal/Core/Entity/Plugin/DataType/FieldItem.php
+++ b/core/lib/Drupal/Core/Entity/Plugin/DataType/FieldItem.php
@@ -19,7 +19,7 @@
  * @DataType(
  *   id = "field_item",
  *   label = @Translation("Field item"),
- *   list_class = "\Drupal\Core\Entity\Field\FieldItemList",
+ *   list_class = "\Drupal\Core\Entity\Plugin\DataType\FieldItemList",
  *   derivative = "Drupal\Core\Entity\Plugin\DataType\Deriver\FieldItemDeriver"
  * )
  */
diff --git a/core/lib/Drupal/Core/Entity/Plugin/DataType/FieldItemList.php b/core/lib/Drupal/Core/Entity/Plugin/DataType/FieldItemList.php
index b3ce264..561aa1d 100644
--- a/core/lib/Drupal/Core/Entity/Plugin/DataType/FieldItemList.php
+++ b/core/lib/Drupal/Core/Entity/Plugin/DataType/FieldItemList.php
@@ -7,14 +7,21 @@
 
 namespace Drupal\Core\Entity\Plugin\DataType;
 
+use Drupal\Core\Entity\Field\FieldItemListInterface;
+use Drupal\Core\Session\AccountInterface;
+use Drupal\Core\TypedData\TypedDataInterface;
+use Drupal\Core\TypedData\Plugin\DataType\ItemList;
+use Drupal\Core\Language\Language;
 use Drupal\Core\TypedData\Annotation\DataType;
 use Drupal\Core\Annotation\Translation;
-use Drupal\Core\Entity\Field\FieldItemList as ExistingFieldItemList;
 
 /**
  * Defines a data type plugin for entity fields, i.e. the list of field items.
  *
- * @todo: Move the whole implementation to this place.
+ * An entity field is a list of field items, containing various field item
+ * properties. Note that even single-valued entity fields are represented as
+ * list of field items, however for easy access to the contained item the entity
+ * field delegates __get() and __set() calls directly to the first item.
  *
  * @DataType(
  *   id = "entity_field",
@@ -22,6 +29,259 @@
  *   class = "\Drupal\Core\Entity\Field\Field"
  * )
  */
-class FieldItemList extends ExistingFieldItemList {
+class FieldItemList extends ItemList implements FieldItemListInterface {
+
+  /**
+   * Numerically indexed array of field items, implementing the
+   * FieldItemInterface.
+   *
+   * @var array
+   */
+  protected $list = array();
+
+  /**
+   * The langcode of the field values held in the object.
+   *
+   * @var string
+   */
+  protected $langcode = Language::LANGCODE_DEFAULT;
+
+  /**
+   * Overrides TypedData::__construct().
+   */
+  public function __construct($definition, $name = NULL, TypedDataInterface $parent = NULL) {
+    parent::__construct($definition, $name, $parent);
+    $this->definition['field_name'] = $name;
+    // Always initialize one empty item as most times a value for at least one
+    // item will be present. That way prototypes created by
+    // \Drupal\Core\TypedData\TypedDataManager::getPropertyInstance() will
+    // already have this field item ready for use after cloning.
+    $this->list[0] = $this->createItem(0);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getEntity() {
+    return $this->getParent();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setLangcode($langcode) {
+    $this->langcode = $langcode;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getLangcode() {
+    return $this->langcode;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFieldDefinition() {
+    return $this->definition;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function filterEmptyValues() {
+    if (isset($this->list)) {
+      $this->list = array_values(array_filter($this->list, function($item) {
+        return !$item->isEmpty();
+      }));
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   * @todo Revisit the need when all entity types are converted to NG entities.
+   */
+  public function getValue($include_computed = FALSE) {
+    if (isset($this->list)) {
+      $values = array();
+      foreach ($this->list as $delta => $item) {
+        $values[$delta] = $item->getValue($include_computed);
+      }
+      return $values;
+    }
+  }
+
+  /**
+   * Overrides \Drupal\Core\TypedData\Plugin\DataType\ItemList::setValue().
+   */
+  public function setValue($values, $notify = TRUE) {
+    if (!isset($values) || $values === array()) {
+      $this->list = $values;
+    }
+    else {
+      // Support passing in only the value of the first item.
+      if (!is_array($values) || !is_numeric(current(array_keys($values)))) {
+        $values = array(0 => $values);
+      }
+
+      // Clear the values of properties for which no value has been passed.
+      if (isset($this->list)) {
+        $this->list = array_intersect_key($this->list, $values);
+      }
+
+      // Set the values.
+      foreach ($values as $delta => $value) {
+        if (!is_numeric($delta)) {
+          throw new \InvalidArgumentException('Unable to set a value with a non-numeric delta in a list.');
+        }
+        elseif (!isset($this->list[$delta])) {
+          $this->list[$delta] = $this->createItem($delta, $value);
+        }
+        else {
+          $this->list[$delta]->setValue($value, FALSE);
+        }
+      }
+    }
+    // Notify the parent of any changes.
+    if ($notify && isset($this->parent)) {
+      $this->parent->onChange($this->name);
+    }
+  }
+
+  /**
+   * Implements \Drupal\Core\Entity\Field\FieldItemListInterface::getPropertyDefinition().
+   */
+  public function getPropertyDefinition($name) {
+    return $this->offsetGet(0)->getPropertyDefinition($name);
+  }
+
+  /**
+   * Implements \Drupal\Core\Entity\Field\FieldItemListInterface::getPropertyDefinitions().
+   */
+  public function getPropertyDefinitions() {
+    return $this->offsetGet(0)->getPropertyDefinitions();
+  }
+
+  /**
+   * Implements \Drupal\Core\Entity\Field\FieldItemListInterface::__get().
+   */
+  public function __get($property_name) {
+    return $this->offsetGet(0)->__get($property_name);
+  }
+
+  /**
+   * Implements \Drupal\Core\Entity\Field\FieldItemListInterface::get().
+   */
+  public function get($property_name) {
+    return $this->offsetGet(0)->get($property_name);
+  }
+
+  /**
+   * Implements \Drupal\Core\Entity\Field\FieldItemListInterface::__set().
+   */
+  public function __set($property_name, $value) {
+    $this->offsetGet(0)->__set($property_name, $value);
+  }
+
+  /**
+   * Implements \Drupal\Core\Entity\Field\FieldItemListInterface::__isset().
+   */
+  public function __isset($property_name) {
+    return $this->offsetGet(0)->__isset($property_name);
+  }
+
+  /**
+   * Implements \Drupal\Core\Entity\Field\FieldItemListInterface::__unset().
+   */
+  public function __unset($property_name) {
+    return $this->offsetGet(0)->__unset($property_name);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function access($operation = 'view', AccountInterface $account = NULL) {
+    $access_controller = \Drupal::entityManager()->getAccessController($this->getParent()->entityType());
+    return $access_controller->fieldAccess($operation, $this->getFieldDefinition(), $account, $this);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function defaultAccess($operation = 'view', AccountInterface $account = NULL) {
+    // Grant access per default.
+    return TRUE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function applyDefaultValue($notify = TRUE) {
+    $value = $this->getFieldDefinition()->getFieldDefaultValue($this->getEntity());
+
+    // NULL or array() mean "no default value", but  0, '0' and the empty string
+    // are valid default values.
+    if (!isset($value) || (is_array($value) && empty($value))) {
+      // Create one field item and apply defaults.
+      $this->offsetGet(0)->applyDefaultValue(FALSE);
+    }
+    else {
+      $this->setValue($value, $notify);
+    }
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function preSave() {
+    // Filter out empty items.
+    $this->filterEmptyValues();
+
+    $this->delegateMethod('presave');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function insert() {
+    $this->delegateMethod('insert');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function update() {
+    $this->delegateMethod('update');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function delete() {
+    $this->delegateMethod('delete');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function deleteRevision() {
+    $this->delegateMethod('deleteRevision');
+  }
+
+  /**
+   * Calls a method on each FieldItem.
+   *
+   * @param string $method
+   *   The name of the method.
+   */
+  protected function delegateMethod($method) {
+    if (isset($this->list)) {
+      foreach ($this->list as $item) {
+        $item->{$method}();
+      }
+    }
+  }
 
 }
diff --git a/core/lib/Drupal/Core/Entity/Plugin/DataType/IntegerItem.php b/core/lib/Drupal/Core/Entity/Plugin/DataType/IntegerItem.php
index 6bd8cf8..29cbe40 100644
--- a/core/lib/Drupal/Core/Entity/Plugin/DataType/IntegerItem.php
+++ b/core/lib/Drupal/Core/Entity/Plugin/DataType/IntegerItem.php
@@ -18,7 +18,7 @@
  *   id = "integer_field",
  *   label = @Translation("Integer field item"),
  *   description = @Translation("An entity field containing an integer value."),
- *   list_class = "\Drupal\Core\Entity\Field\FieldItemList"
+ *   list_class = "\Drupal\Core\Entity\Plugin\DataType\FieldItemList"
  * )
  */
 class IntegerItem extends FieldItemBase {
diff --git a/core/lib/Drupal/Core/Entity/Plugin/DataType/LanguageItem.php b/core/lib/Drupal/Core/Entity/Plugin/DataType/LanguageItem.php
index b156a34..42f12a1 100644
--- a/core/lib/Drupal/Core/Entity/Plugin/DataType/LanguageItem.php
+++ b/core/lib/Drupal/Core/Entity/Plugin/DataType/LanguageItem.php
@@ -19,7 +19,7 @@
  *   id = "language_field",
  *   label = @Translation("Language field item"),
  *   description = @Translation("An entity field referencing a language."),
- *   list_class = "\Drupal\Core\Entity\Field\FieldItemList",
+ *   list_class = "\Drupal\Core\Entity\Plugin\DataType\FieldItemList",
  *   constraints = {
  *     "ComplexData" = {
  *       "value" = {"Length" = {"max" = 12}}
diff --git a/core/lib/Drupal/Core/Entity/Plugin/DataType/StringItem.php b/core/lib/Drupal/Core/Entity/Plugin/DataType/StringItem.php
index a243567..572cc86 100644
--- a/core/lib/Drupal/Core/Entity/Plugin/DataType/StringItem.php
+++ b/core/lib/Drupal/Core/Entity/Plugin/DataType/StringItem.php
@@ -18,7 +18,7 @@
  *   id = "string_field",
  *   label = @Translation("String field item"),
  *   description = @Translation("An entity field containing a string value."),
- *   list_class = "\Drupal\Core\Entity\Field\FieldItemList"
+ *   list_class = "\Drupal\Core\Entity\Plugin\DataType\FieldItemList"
  * )
  */
 class StringItem extends FieldItemBase {
diff --git a/core/lib/Drupal/Core/Entity/Plugin/DataType/UriItem.php b/core/lib/Drupal/Core/Entity/Plugin/DataType/UriItem.php
index 6ce5970..3e3ae0a 100644
--- a/core/lib/Drupal/Core/Entity/Plugin/DataType/UriItem.php
+++ b/core/lib/Drupal/Core/Entity/Plugin/DataType/UriItem.php
@@ -18,7 +18,7 @@
  *   id = "uri_field",
  *   label = @Translation("URI field item"),
  *   description = @Translation("An entity field containing a URI."),
- *   list_class = "\Drupal\Core\Entity\Field\FieldItemList"
+ *   list_class = "\Drupal\Core\Entity\Plugin\DataType\FieldItemList"
  * )
  */
 class UriItem extends FieldItemBase {
diff --git a/core/lib/Drupal/Core/Entity/Plugin/DataType/UuidItem.php b/core/lib/Drupal/Core/Entity/Plugin/DataType/UuidItem.php
index 3e28741..3b0b2a6 100644
--- a/core/lib/Drupal/Core/Entity/Plugin/DataType/UuidItem.php
+++ b/core/lib/Drupal/Core/Entity/Plugin/DataType/UuidItem.php
@@ -19,7 +19,7 @@
  *   id = "uuid_field",
  *   label = @Translation("UUID field item"),
  *   description = @Translation("An entity field containing a UUID."),
- *   list_class = "\Drupal\Core\Entity\Field\FieldItemList",
+ *   list_class = "\Drupal\Core\Entity\Plugin\DataType\FieldItemList",
  *   constraints = {
  *     "ComplexData" = {
  *       "value" = {"Length" = {"max" = 128}}
diff --git a/core/lib/Drupal/Core/TypedData/DataDefinition.php b/core/lib/Drupal/Core/TypedData/DataDefinition.php
index e7016c7..0bb3ee5 100644
--- a/core/lib/Drupal/Core/TypedData/DataDefinition.php
+++ b/core/lib/Drupal/Core/TypedData/DataDefinition.php
@@ -20,6 +20,16 @@ class DataDefinition implements DataDefinitionInterface, \ArrayAccess {
   protected $definition = array();
 
   /**
+   * Creates a new data definition.
+   *
+   * @return \Drupal\Core\TypedData\DataDefinition
+   */
+  public static function create() {
+    $class = get_called_class();
+    return new $class();
+  }
+
+  /**
    * Constructs a new data definition object.
    *
    * @param array $definition
@@ -334,7 +344,9 @@ public static function createFromOldStyleDefinition(array $definition) {
       }
     }
 
-    // Take care of the item definition.
+    // Take care of the item definition now. 'required' applies to the list
+    // definition.
+    unset($definition['required']);
     $item_definition = new DataDefinition($definition);
     if (isset($definition['settings'])) {
       $item_definition->setSettings($definition['settings']);
diff --git a/core/lib/Drupal/Core/TypedData/ListDefinition.php b/core/lib/Drupal/Core/TypedData/ListDefinition.php
index fc6b557..d192e84 100644
--- a/core/lib/Drupal/Core/TypedData/ListDefinition.php
+++ b/core/lib/Drupal/Core/TypedData/ListDefinition.php
@@ -20,6 +20,16 @@ class ListDefinition extends DataDefinition implements ListDefinitionInterface {
   protected $itemDefinition;
 
   /**
+   * Creates a new list definition.
+   *
+   * @return \Drupal\Core\TypedData\ListDefinition
+   */
+  public static function create() {
+    $class = get_called_class();
+    return new $class();
+  }
+
+  /**
    * {@inheritdoc}
    */
   public function __construct(array $definition = array()) {
diff --git a/core/lib/Drupal/Core/TypedData/Plugin/DataType/ItemList.php b/core/lib/Drupal/Core/TypedData/Plugin/DataType/ItemList.php
index 5bb8b90..e7dca89 100644
--- a/core/lib/Drupal/Core/TypedData/Plugin/DataType/ItemList.php
+++ b/core/lib/Drupal/Core/TypedData/Plugin/DataType/ItemList.php
@@ -101,18 +101,6 @@ public function getString() {
   }
 
   /**
-   * Overrides \Drupal\Core\TypedData\TypedData::getConstraints().
-   */
-  public function getConstraints() {
-    if (isset($this->definition['item_definition']) && isset($this->definition['constraints'])) {
-      return $this->definition['constraints'];
-    }
-    // BC: If no item definition is specified, we apply possibly specified
-    // constraints to the list items only.
-    return array();
-  }
-
-  /**
    * Implements \ArrayAccess::offsetExists().
    */
   public function offsetExists($offset) {
diff --git a/core/lib/Drupal/Core/TypedData/TypedDataManager.php b/core/lib/Drupal/Core/TypedData/TypedDataManager.php
index 107ad2f..0850e37 100644
--- a/core/lib/Drupal/Core/TypedData/TypedDataManager.php
+++ b/core/lib/Drupal/Core/TypedData/TypedDataManager.php
@@ -314,17 +314,19 @@ public function getValidationConstraintManager() {
    * @see \Drupal\Core\Validation\ConstraintManager
    *
    * @param \Drupal\Core\TypedData\DataDefinitionInterface $definition
-   *   A data definition array.
+   *   A data definition.
    *
    * @return array
    *   Array of constraints, each being an instance of
    *   \Symfony\Component\Validator\Constraint.
+   *
+   * @todo: Having this as well as $definition->getConstraints() is confusing.
    */
-  public function getConstraints($definition) {
+  public function getConstraints(DataDefinitionInterface $definition) {
     $constraints = array();
     $validation_manager = $this->getValidationConstraintManager();
 
-    $type_definition = $this->getDefinition($definition['type']);
+    $type_definition = $this->getDefinition($definition->getDataType());
     // Auto-generate a constraint for data types implementing a primitive
     // interface.
     if (is_subclass_of($type_definition['class'], '\Drupal\Core\TypedData\PrimitiveInterface')) {
@@ -341,19 +343,21 @@ public function getConstraints($definition) {
       }
     }
     // Add any constraints specified as part of the data definition.
-    if (isset($definition['constraints'])) {
-      foreach ($definition['constraints'] as $name => $options) {
-        $constraints[] = $validation_manager->create($name, $options);
-      }
+    $defined_constraints = $definition->getConstraints();
+    foreach ($defined_constraints as $name => $options) {
+      $constraints[] = $validation_manager->create($name, $options);
     }
     // Add the NotNull constraint for required data.
-    if (!empty($definition['required']) && empty($definition['constraints']['NotNull'])) {
+    if ($definition->isRequired() && !isset($defined_constraints['NotNull'])) {
       $constraints[] = $validation_manager->create('NotNull', array());
     }
 
     // If the definition does not provide a class use the class from the type
     // definition for performing interface checks.
-    $class = isset($definition['class']) ? $definition['class'] : $type_definition['class'];
+    $class = $definition->getClass();
+    if (!$class) {
+      $class = $type_definition['class'];
+    }
     // Check if the class provides allowed values.
     if (array_key_exists('Drupal\Core\TypedData\AllowedValuesInterface', class_implements($class))) {
       $constraints[] = $validation_manager->create('AllowedValues', array());
diff --git a/core/modules/field/lib/Drupal/field/Plugin/Type/FieldType/ConfigFieldItemList.php b/core/modules/field/lib/Drupal/field/Plugin/Type/FieldType/ConfigFieldItemList.php
index 90555cf..1a2a6d0 100644
--- a/core/modules/field/lib/Drupal/field/Plugin/Type/FieldType/ConfigFieldItemList.php
+++ b/core/modules/field/lib/Drupal/field/Plugin/Type/FieldType/ConfigFieldItemList.php
@@ -7,9 +7,8 @@
 
 namespace Drupal\field\Plugin\Type\FieldType;
 
-use Drupal\Core\TypedData\DataDefinitionInterface;
 use Drupal\Core\TypedData\TypedDataInterface;
-use Drupal\Core\Entity\Field\FieldItemList;
+use Drupal\Core\Entity\Plugin\DataType\FieldItemList;
 use Drupal\field\Field as FieldAPI;
 
 /**
diff --git a/core/modules/path/lib/Drupal/path/Plugin/DataType/PathItem.php b/core/modules/path/lib/Drupal/path/Plugin/DataType/PathItem.php
index 11059b5..7a0f9fe 100644
--- a/core/modules/path/lib/Drupal/path/Plugin/DataType/PathItem.php
+++ b/core/modules/path/lib/Drupal/path/Plugin/DataType/PathItem.php
@@ -18,7 +18,7 @@
  *   id = "path_field",
  *   label = @Translation("Path field item"),
  *   description = @Translation("An entity field containing a path alias and related data."),
- *   list_class = "\Drupal\Core\Entity\Field\FieldItemList"
+ *   list_class = "\Drupal\Core\Entity\Plugin\DataType\FieldItemList"
  * )
  */
 class PathItem extends FieldItemBase {
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/Entity/Term.php b/core/modules/taxonomy/lib/Drupal/taxonomy/Entity/Term.php
index 066e8f2..ed707fa 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/Entity/Term.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/Entity/Term.php
@@ -11,7 +11,9 @@
 use Drupal\Core\Entity\Annotation\EntityType;
 use Drupal\Core\Entity\EntityStorageControllerInterface;
 use Drupal\Core\Annotation\Translation;
+use Drupal\Core\Entity\Field\FieldDefinition;
 use Drupal\Core\Language\Language;
+use Drupal\Core\TypedData\DataDefinition;
 use Drupal\taxonomy\TermInterface;
 
 /**
@@ -203,67 +205,66 @@ public function postSave(EntityStorageControllerInterface $storage_controller, $
    * {@inheritdoc}
    */
   public static function baseFieldDefinitions($entity_type) {
-    $properties['tid'] = array(
-      'label' => t('Term ID'),
-      'description' => t('The term ID.'),
-      'type' => 'integer_field',
-      'read-only' => TRUE,
-    );
-    $properties['uuid'] = array(
-      'label' => t('UUID'),
-      'description' => t('The term UUID.'),
-      'type' => 'uuid_field',
-      'read-only' => TRUE,
-    );
-    $properties['vid'] = array(
-      'label' => t('Vocabulary ID'),
-      'description' => t('The ID of the vocabulary to which the term is assigned.'),
-      'type' => 'string_field',
-    );
-    $properties['langcode'] = array(
-      'label' => t('Language code'),
-      'description' => t('The term language code.'),
-      'type' => 'language_field',
-    );
-    $properties['name'] = array(
-      'label' => t('Name'),
-      'description' => t('The term name.'),
-      'type' => 'string_field',
-    );
-    $properties['description'] = array(
-      'label' => t('Description'),
-      'description' => t('A description of the term'),
-      'type' => 'string_field',
-    );
+
+    $fields['tid'] = FieldDefinition::create()
+      ->setLabel(t('Term ID'))
+      ->setDescription(t('The term ID.'))
+      ->setFieldType('integer')
+      ->setReadOnly(TRUE);
+
+    $fields['uuid'] = FieldDefinition::create()
+      ->setLabel(t('UUID'))
+      ->setDescription(t('The term UUID.'))
+      ->setFieldType('uuid')
+      ->setReadOnly(TRUE);
+
+    $fields['vid'] = FieldDefinition::create()
+      ->setLabel(t('Vocabulary ID'))
+      ->setDescription(t('The ID of the vocabulary to which the term is assigned.'))
+      ->setFieldType('string');
+
+    $fields['langcode'] = FieldDefinition::create()
+      ->setLabel(t('Language code'))
+      ->setDescription(t('The term language code.'))
+      ->setFieldType('language');
+
+    $fields['name'] = FieldDefinition::create()
+      ->setLabel(t('Name'))
+      ->setDescription(t('The term name.'))
+      ->setFieldType('string');
+
+    $fields['description'] = FieldDefinition::create()
+      ->setLabel(t('Description'))
+      ->setDescription(t('A description of the term.'))
+      ->setFieldType('string');
+
     // @todo Combine with description.
-    $properties['format'] = array(
-      'label' => t('Description format'),
-      'description' => t('The filter format ID of the description.'),
-      'type' => 'string_field',
-    );
-    $properties['weight'] = array(
-      'label' => t('Weight'),
-      'description' => t('The weight of this term in relation to other terms.'),
-      'type' => 'integer_field',
-      'settings' => array('default_value' => 0),
-    );
-    $properties['parent'] = array(
-      'label' => t('Term Parents'),
-      'description' => t('The parents of this term.'),
-      'type' => 'integer_field',
+    $fields['format'] = FieldDefinition::create()
+      ->setLabel(t('Description format'))
+      ->setDescription(t('The filter format ID of the description.'))
+      ->setFieldType('string');
+
+    $fields['weight'] = FieldDefinition::create()
+      ->setLabel(t('Weight'))
+      ->setDescription(t('The weight of this term in relation to other terms.'))
+      ->setFieldType('integer')
+      ->setFieldSetting('default_value', 0);
+
+    $fields['parent'] = FieldDefinition::create()
+      ->setLabel(t('Term Parents'))
+      ->setDescription(t('The parents of this term.'))
+      ->setFieldType('integer')
       // Save new terms with no parents by default.
-      'settings' => array('default_value' => 0),
-      'computed' => TRUE,
-    );
-    $properties['changed'] = array(
-      'label' => t('Changed'),
-      'description' => t('The time that the term was last edited.'),
-      'type' => 'integer_field',
-      'property_constraints' => array(
-        'value' => array('EntityChanged' => array()),
-      ),
-    );
-    return $properties;
+      ->setFieldSetting('default_value', 0)
+      ->setComputed(TRUE);
+
+    $fields['changed'] = FieldDefinition::create()
+      ->setLabel(t('Changed'))
+      ->setDescription(t('The time that the term was last edited.'))
+      ->setFieldType('integer')
+      ->setPropertyConstraints('value', array('EntityChanged' => array()));
+
+    return $fields;
   }
 
   /**
diff --git a/core/modules/text/lib/Drupal/text/TextProcessed.php b/core/modules/text/lib/Drupal/text/TextProcessed.php
index eee8cc8..dd1fe8e 100644
--- a/core/modules/text/lib/Drupal/text/TextProcessed.php
+++ b/core/modules/text/lib/Drupal/text/TextProcessed.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\text;
 
-use Drupal\Core\TypedData\DataDefinitionInterface;
 use Drupal\Core\TypedData\TypedDataInterface;
 use Drupal\Core\TypedData\TypedData;
 use Drupal\Core\TypedData\ReadOnlyException;