diff --git a/core/lib/Drupal/Core/Action/ActionBag.php b/core/lib/Drupal/Core/Action/ActionBag.php
deleted file mode 100644
index a8210fe..0000000
--- a/core/lib/Drupal/Core/Action/ActionBag.php
+++ /dev/null
@@ -1,52 +0,0 @@
-<?php
-
-/**
- * @file
- * Contains \Drupal\Core\Action\ActionBag.
- */
-
-namespace Drupal\Core\Action;
-
-use Drupal\Component\Plugin\PluginBag;
-use Drupal\Component\Plugin\PluginManagerInterface;
-
-/**
- * Provides a container for lazily loading Action plugins.
- */
-class ActionBag extends PluginBag {
-
-  /**
-   * The manager used to instantiate the plugins.
-   *
-   * @var \Drupal\Component\Plugin\PluginManagerInterface
-   */
-  protected $manager;
-
-  /**
-   * Constructs a new ActionBag object.
-   *
-   * @param \Drupal\Component\Plugin\PluginManagerInterface $manager
-   *   The manager to be used for instantiating plugins.
-   * @param array $instance_ids
-   *   The ids of the plugin instances with which we are dealing.
-   * @param array $configuration
-   *   An array of configuration.
-   */
-  public function __construct(PluginManagerInterface $manager, array $instance_ids, array $configuration) {
-    $this->manager = $manager;
-    $this->instanceIDs = drupal_map_assoc($instance_ids);
-    $this->configuration = $configuration;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  protected function initializePlugin($instance_id) {
-    if (isset($this->pluginInstances[$instance_id])) {
-      return;
-    }
-
-    $this->pluginInstances[$instance_id] = $this->manager->createInstance($instance_id, $this->configuration);
-  }
-
-}
diff --git a/core/lib/Drupal/Core/Action/ConfigurableActionBase.php b/core/lib/Drupal/Core/Action/ConfigurableActionBase.php
index 04ca4fe..b2c389a 100644
--- a/core/lib/Drupal/Core/Action/ConfigurableActionBase.php
+++ b/core/lib/Drupal/Core/Action/ConfigurableActionBase.php
@@ -7,13 +7,13 @@
 
 namespace Drupal\Core\Action;
 
-use Drupal\Core\Action\ConfigurableActionInterface;
+use Drupal\Core\Plugin\ConfigurablePluginInterface;
 use Drupal\Core\Action\ActionBase;
 
 /**
  * Provides a base implementation for a configurable Action plugin.
  */
-abstract class ConfigurableActionBase extends ActionBase implements ConfigurableActionInterface {
+abstract class ConfigurableActionBase extends ActionBase implements ConfigurablePluginInterface {
 
   /**
    * {@inheritdoc}
@@ -43,7 +43,7 @@ public function getConfiguration() {
   /**
    * {@inheritdoc}
    */
-  public function validate(array &$form, array &$form_state) {
+  public function validateConfigurationForm(array &$form, array &$form_state) {
   }
 
 }
diff --git a/core/lib/Drupal/Core/Action/ConfigurableActionInterface.php b/core/lib/Drupal/Core/Plugin/ConfigurablePluginInterface.php
similarity index 58%
rename from core/lib/Drupal/Core/Action/ConfigurableActionInterface.php
rename to core/lib/Drupal/Core/Plugin/ConfigurablePluginInterface.php
index c0a66a9..ec5519b 100644
--- a/core/lib/Drupal/Core/Action/ConfigurableActionInterface.php
+++ b/core/lib/Drupal/Core/Plugin/ConfigurablePluginInterface.php
@@ -2,26 +2,22 @@
 
 /**
  * @file
- * Contains \Drupal\Core\Action\ConfigurableActionInterface.
+ * Contains \Drupal\Core\Plugin\ConfigurablePluginInterface.
  */
 
-namespace Drupal\Core\Action;
+namespace Drupal\Core\Plugin;
 
-use Drupal\Core\Action\ActionInterface;
 
 /**
- * Provides an interface for an Action plugin.
- *
- * @see \Drupal\Core\Annotation\Operation
- * @see \Drupal\Core\Action\OperationManager
+ * Provides an interface for a configurable plugin.
  */
-interface ConfigurableActionInterface extends ActionInterface {
+interface ConfigurablePluginInterface {
 
   /**
    * Returns this plugin's configuration.
    *
    * @return array
-   *   An array of this action plugin's configuration.
+   *   An array of this plugin's configuration.
    */
   public function getConfiguration();
 
@@ -36,7 +32,7 @@ public function getConfiguration();
    * @return array
    *   The form structure.
    */
-  public function form(array $form, array &$form_state);
+  public function buildConfigurationForm(array $form, array &$form_state);
 
   /**
    * Form validation handler.
@@ -46,16 +42,21 @@ public function form(array $form, array &$form_state);
    * @param array $form_state
    *   An associative array containing the current state of the form.
    */
-  public function validate(array &$form, array &$form_state);
+  public function validateConfigurationForm(array &$form, array &$form_state);
 
   /**
    * Form submission handler.
    *
+   * To properly store submitted form values store them in $this->configuration.
+   * @code
+   *   $this->configuration['some_value'] = $form_state['values']['some_value'];
+   * @endcode
+   *
    * @param array $form
    *   An associative array containing the structure of the form.
    * @param array $form_state
    *   An associative array containing the current state of the form.
    */
-  public function submit(array &$form, array &$form_state);
+  public function submitConfigurationForm(array &$form, array &$form_state);
 
 }
diff --git a/core/lib/Drupal/Core/Plugin/DefaultSinglePluginBag.php b/core/lib/Drupal/Core/Plugin/DefaultSinglePluginBag.php
new file mode 100644
index 0000000..561dc99
--- /dev/null
+++ b/core/lib/Drupal/Core/Plugin/DefaultSinglePluginBag.php
@@ -0,0 +1,63 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Plugin\DefaultSinglePluginBag.
+ */
+
+namespace Drupal\Core\Plugin;
+
+use Drupal\Component\Plugin\PluginBag;
+use Drupal\Component\Plugin\PluginManagerInterface;
+
+/**
+ * Provides a default plugin bag for a plugin type.
+ *
+ * A plugin bag usually stores multiple plugins, and is used to lazily
+ * instantiate them. When only one plugin is needed, it is still best practice
+ * to encapsulate all of the instantiation logic in a plugin bag. This class can
+ * be used directly, or subclassed to add further exception handling in
+ * self::initializePlugin().
+ */
+class DefaultSinglePluginBag extends PluginBag {
+
+  /**
+   * The manager used to instantiate the plugins.
+   *
+   * @var \Drupal\Component\Plugin\PluginManagerInterface
+   */
+  protected $manager;
+
+  /**
+   * An array of configuration to instantiate the plugin with.
+   *
+   * @var array
+   */
+  protected $configuration;
+
+  /**
+   * Constructs a new DefaultSinglePluginBag object.
+   *
+   * @param \Drupal\Component\Plugin\PluginManagerInterface $manager
+   *   The manager to be used for instantiating plugins.
+   * @param array $instance_ids
+   *   The IDs of the plugin instances with which we are dealing.
+   * @param array $configuration
+   *   An array of configuration.
+   */
+  public function __construct(PluginManagerInterface $manager, array $instance_ids, array $configuration) {
+    $this->manager = $manager;
+    $this->instanceIDs = drupal_map_assoc($instance_ids);
+    $this->configuration = $configuration;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function initializePlugin($instance_id) {
+    if (!isset($this->pluginInstances[$instance_id])) {
+      $this->pluginInstances[$instance_id] = $this->manager->createInstance($instance_id, $this->configuration);
+    }
+  }
+
+}
diff --git a/core/modules/action/lib/Drupal/action/ActionFormControllerBase.php b/core/modules/action/lib/Drupal/action/ActionFormControllerBase.php
index ff48164..3655e7b 100644
--- a/core/modules/action/lib/Drupal/action/ActionFormControllerBase.php
+++ b/core/modules/action/lib/Drupal/action/ActionFormControllerBase.php
@@ -10,7 +10,7 @@
 use Drupal\Core\Entity\EntityControllerInterface;
 use Drupal\Core\Entity\EntityFormController;
 use Drupal\Core\Extension\ModuleHandlerInterface;
-use Drupal\Core\Action\ConfigurableActionInterface;
+use Drupal\Core\Plugin\ConfigurablePluginInterface;
 use Drupal\Core\Entity\EntityStorageControllerInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
@@ -97,8 +97,8 @@ public function form(array $form, array &$form_state) {
       '#value' => $this->entity->getType(),
     );
 
-    if ($this->plugin instanceof ConfigurableActionInterface) {
-      $form += $this->plugin->form($form, $form_state);
+    if ($this->plugin instanceof ConfigurablePluginInterface) {
+      $form += $this->plugin->buildConfigurationForm($form, $form_state);
     }
 
     return parent::form($form, $form_state);
@@ -133,8 +133,8 @@ protected function actions(array $form, array &$form_state) {
   public function validate(array $form, array &$form_state) {
     parent::validate($form, $form_state);
 
-    if ($this->plugin instanceof ConfigurableActionInterface) {
-      $this->plugin->validate($form, $form_state);
+    if ($this->plugin instanceof ConfigurablePluginInterface) {
+      $this->plugin->validateConfigurationForm($form, $form_state);
     }
   }
 
@@ -144,8 +144,8 @@ public function validate(array $form, array &$form_state) {
   public function submit(array $form, array &$form_state) {
     parent::submit($form, $form_state);
 
-    if ($this->plugin instanceof ConfigurableActionInterface) {
-      $this->plugin->submit($form, $form_state);
+    if ($this->plugin instanceof ConfigurablePluginInterface) {
+      $this->plugin->submitConfigurationForm($form, $form_state);
     }
     return $this->entity;
   }
diff --git a/core/modules/action/lib/Drupal/action/Form/ActionAdminManageForm.php b/core/modules/action/lib/Drupal/action/Form/ActionAdminManageForm.php
index d0244b1..3fbdda7 100644
--- a/core/modules/action/lib/Drupal/action/Form/ActionAdminManageForm.php
+++ b/core/modules/action/lib/Drupal/action/Form/ActionAdminManageForm.php
@@ -57,7 +57,7 @@ public function getFormID() {
   public function buildForm(array $form, array &$form_state) {
     $actions = array();
     foreach ($this->manager->getDefinitions() as $id => $definition) {
-      if (is_subclass_of($definition['class'], '\Drupal\Core\Action\ConfigurableActionInterface')) {
+      if (is_subclass_of($definition['class'], '\Drupal\Core\Plugin\ConfigurablePluginInterface')) {
         $key = Crypt::hashBase64($id);
         $actions[$key] = $definition['label'] . '...';
       }
diff --git a/core/modules/action/lib/Drupal/action/Plugin/Action/EmailAction.php b/core/modules/action/lib/Drupal/action/Plugin/Action/EmailAction.php
index 43908b0..77e5f21 100644
--- a/core/modules/action/lib/Drupal/action/Plugin/Action/EmailAction.php
+++ b/core/modules/action/lib/Drupal/action/Plugin/Action/EmailAction.php
@@ -116,7 +116,7 @@ protected function getDefaultConfiguration() {
   /**
    * {@inheritdoc}
    */
-  public function form(array $form, array &$form_state) {
+  public function buildConfigurationForm(array $form, array &$form_state) {
     $form['recipient'] = array(
       '#type' => 'textfield',
       '#title' => t('Recipient'),
@@ -145,7 +145,7 @@ public function form(array $form, array &$form_state) {
   /**
    * {@inheritdoc}
    */
-  public function validate(array &$form, array &$form_state) {
+  public function validateConfigurationForm(array &$form, array &$form_state) {
     if (!valid_email_address($form_state['values']['recipient']) && strpos($form_state['values']['recipient'], ':mail') === FALSE) {
       // We want the literal %author placeholder to be emphasized in the error message.
       form_set_error('recipient', t('Enter a valid email address or use a token e-mail address such as %author.', array('%author' => '[node:author:mail]')));
@@ -155,7 +155,7 @@ public function validate(array &$form, array &$form_state) {
   /**
    * {@inheritdoc}
    */
-  public function submit(array &$form, array &$form_state) {
+  public function submitConfigurationForm(array &$form, array &$form_state) {
     $this->configuration['recipient'] = $form_state['values']['recipient'];
     $this->configuration['subject'] = $form_state['values']['subject'];
     $this->configuration['message'] = $form_state['values']['message'];
diff --git a/core/modules/action/lib/Drupal/action/Plugin/Action/GotoAction.php b/core/modules/action/lib/Drupal/action/Plugin/Action/GotoAction.php
index 93a4c87..fd158fb 100644
--- a/core/modules/action/lib/Drupal/action/Plugin/Action/GotoAction.php
+++ b/core/modules/action/lib/Drupal/action/Plugin/Action/GotoAction.php
@@ -96,7 +96,7 @@ protected function getDefaultConfiguration() {
   /**
    * {@inheritdoc}
    */
-  public function form(array $form, array &$form_state) {
+  public function buildConfigurationForm(array $form, array &$form_state) {
     $form['url'] = array(
       '#type' => 'textfield',
       '#title' => t('URL'),
@@ -110,7 +110,7 @@ public function form(array $form, array &$form_state) {
   /**
    * {@inheritdoc}
    */
-  public function submit(array &$form, array &$form_state) {
+  public function submitConfigurationForm(array &$form, array &$form_state) {
     $this->configuration['url'] = $form_state['values']['url'];
   }
 
diff --git a/core/modules/action/lib/Drupal/action/Plugin/Action/MessageAction.php b/core/modules/action/lib/Drupal/action/Plugin/Action/MessageAction.php
index b7f25a2..fef9ab9 100644
--- a/core/modules/action/lib/Drupal/action/Plugin/Action/MessageAction.php
+++ b/core/modules/action/lib/Drupal/action/Plugin/Action/MessageAction.php
@@ -70,7 +70,7 @@ protected function getDefaultConfiguration() {
   /**
    * {@inheritdoc}
    */
-  public function form(array $form, array &$form_state) {
+  public function buildConfigurationForm(array $form, array &$form_state) {
     $form['message'] = array(
       '#type' => 'textarea',
       '#title' => t('Message'),
@@ -85,7 +85,7 @@ public function form(array $form, array &$form_state) {
   /**
    * {@inheritdoc}
    */
-  public function submit(array &$form, array &$form_state) {
+  public function submitConfigurationForm(array &$form, array &$form_state) {
     $this->configuration['message'] = $form_state['values']['message'];
     unset($this->configuration['node']);
   }
diff --git a/core/modules/block/lib/Drupal/block/BlockBase.php b/core/modules/block/lib/Drupal/block/BlockBase.php
index b438dc1..05a90a8 100644
--- a/core/modules/block/lib/Drupal/block/BlockBase.php
+++ b/core/modules/block/lib/Drupal/block/BlockBase.php
@@ -61,7 +61,7 @@ public function settings() {
    *
    * @see \Drupal\Component\Plugin\PluginBase::$configuration
    */
-  public function getConfig() {
+  public function getConfiguration() {
     return $this->configuration;
   }
 
@@ -102,7 +102,7 @@ public function access() {
   }
 
   /**
-   * Implements \Drupal\block\BlockPluginInterface::form().
+   * {@inheritdoc}
    *
    * Creates a generic configuration form for all block types. Individual
    * block plugins can add elements to this form by overriding
@@ -111,7 +111,7 @@ public function access() {
    *
    * @see \Drupal\block\BlockBase::blockForm()
    */
-  public function form($form, &$form_state) {
+  public function buildConfigurationForm(array $form, array &$form_state) {
     $definition = $this->getPluginDefinition();
     $form['module'] = array(
       '#type' => 'value',
@@ -151,14 +151,14 @@ public function form($form, &$form_state) {
    * @return array $form
    *   The renderable form array representing the entire configuration form.
    *
-   * @see \Drupal\block\BlockBase::form()
+   * @see \Drupal\block\BlockBase::buildConfigurationForm()
    */
   public function blockForm($form, &$form_state) {
     return array();
   }
 
   /**
-   * Implements \Drupal\block\BlockPluginInterface::validate().
+   * {@inheritdoc}
    *
    * Most block plugins should not override this method. To add validation
    * for a specific block type, override BlockBase::blockValdiate().
@@ -167,7 +167,7 @@ public function blockForm($form, &$form_state) {
    *
    * @see \Drupal\block\BlockBase::blockValidate()
    */
-  public function validate($form, &$form_state) {
+  public function validateConfigurationForm(array &$form, array &$form_state) {
     $this->blockValidate($form, $form_state);
   }
 
@@ -185,12 +185,12 @@ public function validate($form, &$form_state) {
    *
    * @see \Drupal\block\BlockBase::blockForm()
    * @see \Drupal\block\BlockBase::blockSubmit()
-   * @see \Drupal\block\BlockBase::validate()
+   * @see \Drupal\block\BlockBase::validateConfigurationForm()
    */
   public function blockValidate($form, &$form_state) {}
 
   /**
-   * Implements \Drupal\block\BlockPluginInterface::submit().
+   * {@inheritdoc}
    *
    * Most block plugins should not override this method. To add submission
    * handling for a specific block type, override BlockBase::blockSubmit().
@@ -199,7 +199,7 @@ public function blockValidate($form, &$form_state) {}
    *
    * @see \Drupal\block\BlockBase::blockSubmit()
    */
-  public function submit($form, &$form_state) {
+  public function submitConfigurationForm(array &$form, array &$form_state) {
     if (!form_get_errors()) {
       $this->configuration['label'] = $form_state['values']['label'];
       $this->configuration['label_display'] = $form_state['values']['label_display'];
@@ -222,7 +222,7 @@ public function submit($form, &$form_state) {
    *
    * @see \Drupal\block\BlockBase::blockForm()
    * @see \Drupal\block\BlockBase::blockValidate()
-   * @see \Drupal\block\BlockBase::submit()
+   * @see \Drupal\block\BlockBase::submitConfigurationForm()
    */
   public function blockSubmit($form, &$form_state) {}
 }
diff --git a/core/modules/block/lib/Drupal/block/BlockFormController.php b/core/modules/block/lib/Drupal/block/BlockFormController.php
index f562a68..7789c02 100644
--- a/core/modules/block/lib/Drupal/block/BlockFormController.php
+++ b/core/modules/block/lib/Drupal/block/BlockFormController.php
@@ -25,7 +25,7 @@ public function form(array $form, array &$form_state) {
       '#type' => 'value',
       '#value' => $entity->id(),
     );
-    $form['settings'] = $entity->getPlugin()->form(array(), $form_state);
+    $form['settings'] = $entity->getPlugin()->buildConfigurationForm(array(), $form_state);
 
     $form['machine_name'] = array(
       '#type' => 'machine_name',
@@ -208,7 +208,7 @@ public function validate(array $form, array &$form_state) {
       'values' => &$form_state['values']['settings']
     );
     // Call the plugin validate handler.
-    $entity->getPlugin()->validate($form, $settings);
+    $entity->getPlugin()->validateConfigurationForm($form, $settings);
   }
 
   /**
@@ -224,7 +224,7 @@ public function submit(array $form, array &$form_state) {
       'values' => &$form_state['values']['settings']
     );
     // Call the plugin submit handler.
-    $entity->getPlugin()->submit($form, $settings);
+    $entity->getPlugin()->submitConfigurationForm($form, $settings);
 
     // Save the settings of the plugin.
     $entity->save();
diff --git a/core/modules/block/lib/Drupal/block/BlockPluginBag.php b/core/modules/block/lib/Drupal/block/BlockPluginBag.php
index 5a68beb..3bdb911 100644
--- a/core/modules/block/lib/Drupal/block/BlockPluginBag.php
+++ b/core/modules/block/lib/Drupal/block/BlockPluginBag.php
@@ -7,38 +7,30 @@
 
 namespace Drupal\block;
 
-use Drupal\block\Plugin\Core\Entity\Block;
-use Drupal\Component\Plugin\PluginBag;
-use Drupal\Component\Plugin\PluginManagerInterface;
 use Drupal\Component\Plugin\Exception\PluginException;
+use Drupal\Component\Plugin\PluginManagerInterface;
+use Drupal\Component\Utility\String;
+use Drupal\Core\Plugin\DefaultSinglePluginBag;
 
 /**
  * Provides a collection of block plugins.
  */
-class BlockPluginBag extends PluginBag {
+class BlockPluginBag extends DefaultSinglePluginBag {
 
   /**
-   * The manager used to instantiate the plugins.
+   * The block ID this plugin bag belongs to.
    *
-   * @var \Drupal\Component\Plugin\PluginManagerInterface
+   * @var string
    */
-  protected $manager;
+  protected $blockId;
 
   /**
-   * Constructs a BlockPluginBag object.
-   *
-   * @param \Drupal\Component\Plugin\PluginManagerInterface $manager
-   *   The manager to be used for instantiating plugins.
-   * @param array $instance_ids
-   *   The ids of the plugin instances with which we are dealing.
-   * @param \Drupal\block\Plugin\Core\Entity\Block $entity
-   *   The Block entity that holds our configuration.
+   * {@inheritdoc}
    */
-  public function __construct(PluginManagerInterface $manager, array $instance_ids, Block $entity) {
-    $this->manager = $manager;
-    $this->entity = $entity;
+  public function __construct(PluginManagerInterface $manager, array $instance_ids, array $configuration, $block_id) {
+    parent::__construct($manager, $instance_ids, $configuration);
 
-    $this->instanceIDs = drupal_map_assoc($instance_ids);
+    $this->blockId = $block_id;
   }
 
   /**
@@ -46,18 +38,14 @@ public function __construct(PluginManagerInterface $manager, array $instance_ids
    */
   protected function initializePlugin($instance_id) {
     if (!$instance_id) {
-      throw new PluginException(format_string("The block '@block' did not specify a plugin.", array('@block' => $this->entity->id())));
-    }
-    if (isset($this->pluginInstances[$instance_id])) {
-      return;
+      throw new PluginException(String::format("The block '@block' did not specify a plugin.", array('@block' => $this->blockId)));
     }
 
-    $settings = $this->entity->get('settings');
     try {
-      $this->pluginInstances[$instance_id] = $this->manager->createInstance($instance_id, $settings);
+      parent::initializePlugin($instance_id);
     }
     catch (PluginException $e) {
-      $module = $settings['module'];
+      $module = $this->configuration['module'];
       // Ignore blocks belonging to disabled modules, but re-throw valid
       // exceptions when the module is enabled and the plugin is misconfigured.
       if (!$module || \Drupal::moduleHandler()->moduleExists($module)) {
diff --git a/core/modules/block/lib/Drupal/block/BlockPluginInterface.php b/core/modules/block/lib/Drupal/block/BlockPluginInterface.php
index 1887816..9706763 100644
--- a/core/modules/block/lib/Drupal/block/BlockPluginInterface.php
+++ b/core/modules/block/lib/Drupal/block/BlockPluginInterface.php
@@ -7,6 +7,8 @@
 
 namespace Drupal\block;
 
+use Drupal\Core\Plugin\ConfigurablePluginInterface;
+
 /**
  * Defines the required interface for all block plugins.
  *
@@ -17,7 +19,7 @@
  *
  * @see \Drupal\block\BlockBase
  */
-interface BlockPluginInterface {
+interface BlockPluginInterface extends ConfigurablePluginInterface {
 
   /**
    * Returns the default settings for this block plugin.
@@ -45,54 +47,6 @@ public function settings();
   public function access();
 
   /**
-   * Constructs the block configuration form.
-   *
-   * This method allows base implementations to add a generic configuration
-   * form for extending block plugins.
-   *
-   * @param array $form
-   *   The form definition array for the block configuration form.
-   * @param array $form_state
-   *   An array containing the current state of the configuration form.
-   *
-   * @return array $form
-   *   The renderable form array representing the entire configuration form.
-   *
-   * @see \Drupal\block\BlockFormController::form()
-   * @see \Drupal\block\BlockInterace::validate()
-   * @see \Drupal\block\BlockInterace::submit()
-   */
-  public function form($form, &$form_state);
-
-  /**
-   * Handles form validation for the block configuration form.
-   *
-   * @param array $form
-   *   The form definition array for the block configuration form.
-   * @param array $form_state
-   *   An array containing the current state of the configuration form.
-   *
-   * @see \Drupal\block\BlockFormController::validate()
-   * @see \Drupal\block\BlockInterace::form()
-   * @see \Drupal\block\BlockInterace::submit()
-   */
-  public function validate($form, &$form_state);
-
-  /**
-   * Handles form submissions for the block configuration form.
-   *
-   * @param array $form
-   *   The form definition array for the block configuration form.
-   * @param array $form_state
-   *   An array containing the current state of the configuration form.
-   *
-   * @see \Drupal\block\BlockFormController::submit()
-   * @see \Drupal\block\BlockInterace::form()
-   * @see \Drupal\block\BlockInterace::validate()
-   */
-  public function submit($form, &$form_state);
-
-  /**
    * Builds and returns the renderable array for this block plugin.
    *
    * @return array
diff --git a/core/modules/block/lib/Drupal/block/BlockRenderController.php b/core/modules/block/lib/Drupal/block/BlockRenderController.php
index 45a85d9..57a5d62 100644
--- a/core/modules/block/lib/Drupal/block/BlockRenderController.php
+++ b/core/modules/block/lib/Drupal/block/BlockRenderController.php
@@ -40,7 +40,7 @@ public function viewMultiple(array $entities = array(), $view_mode = 'full', $la
       $plugin_id = $plugin->getPluginId();
 
       if ($content = $plugin->build()) {
-        $configuration = $plugin->getConfig();
+        $configuration = $plugin->getConfiguration();
         $build[$entity_id] = array(
           '#theme' => 'block',
           'content' => $content,
diff --git a/core/modules/block/lib/Drupal/block/Plugin/Core/Entity/Block.php b/core/modules/block/lib/Drupal/block/Plugin/Core/Entity/Block.php
index 1d3cca8..bb3a1d4 100644
--- a/core/modules/block/lib/Drupal/block/Plugin/Core/Entity/Block.php
+++ b/core/modules/block/lib/Drupal/block/Plugin/Core/Entity/Block.php
@@ -105,7 +105,7 @@ class Block extends ConfigEntityBase implements BlockInterface {
   public function __construct(array $values, $entity_type) {
     parent::__construct($values, $entity_type);
 
-    $this->pluginBag = new BlockPluginBag(\Drupal::service('plugin.manager.block'), array($this->plugin), $this);
+    $this->pluginBag = new BlockPluginBag(\Drupal::service('plugin.manager.block'), array($this->plugin), $this->get('settings'), $this->id());
   }
 
   /**
@@ -169,7 +169,7 @@ public function getExportProperties() {
    * {@inheritdoc}
    */
   public function preSave(EntityStorageControllerInterface $storage_controller) {
-    $this->set('settings', $this->getPlugin()->getConfig());
+    $this->set('settings', $this->getPlugin()->getConfiguration());
   }
 
 }
diff --git a/core/modules/block/lib/Drupal/block/Tests/BlockInterfaceTest.php b/core/modules/block/lib/Drupal/block/Tests/BlockInterfaceTest.php
index 327cf45..b3093d9 100644
--- a/core/modules/block/lib/Drupal/block/Tests/BlockInterfaceTest.php
+++ b/core/modules/block/lib/Drupal/block/Tests/BlockInterfaceTest.php
@@ -52,12 +52,12 @@ public function testBlockInterface() {
     );
     // Initial configuration of the block at construction time.
     $display_block = $manager->createInstance('test_block_instantiation', $configuration);
-    $this->assertIdentical($display_block->getConfig(), $expected_configuration, 'The block was configured correctly.');
+    $this->assertIdentical($display_block->getConfiguration(), $expected_configuration, 'The block was configured correctly.');
 
     // Updating an element of the configuration.
     $display_block->setConfig('display_message', 'My custom display message.');
     $expected_configuration['display_message'] = 'My custom display message.';
-    $this->assertIdentical($display_block->getConfig(), $expected_configuration, 'The block configuration was updated correctly.');
+    $this->assertIdentical($display_block->getConfiguration(), $expected_configuration, 'The block configuration was updated correctly.');
 
     $expected_form = array(
       'module' => array(
@@ -85,7 +85,7 @@ public function testBlockInterface() {
     );
     $form_state = array();
     // Ensure there are no form elements that do not belong to the plugin.
-    $this->assertIdentical($display_block->form(array(), $form_state), $expected_form, 'Only the expected form elements were present.');
+    $this->assertIdentical($display_block->buildConfigurationForm(array(), $form_state), $expected_form, 'Only the expected form elements were present.');
 
     $expected_build = array(
       '#children' => 'My custom display message.',
diff --git a/core/modules/block/lib/Drupal/block/Tests/BlockTemplateSuggestionsUnitTest.php b/core/modules/block/lib/Drupal/block/Tests/BlockTemplateSuggestionsUnitTest.php
index 51630ba..3042b5b 100644
--- a/core/modules/block/lib/Drupal/block/Tests/BlockTemplateSuggestionsUnitTest.php
+++ b/core/modules/block/lib/Drupal/block/Tests/BlockTemplateSuggestionsUnitTest.php
@@ -45,7 +45,7 @@ function testBlockThemeHookSuggestions() {
 
     $variables = array();
     $variables['elements']['#block'] = $block;
-    $variables['elements']['#configuration'] = $block->getPlugin()->getConfig();
+    $variables['elements']['#configuration'] = $block->getPlugin()->getConfiguration();
     $variables['elements']['#plugin_id'] = $block->get('plugin');
     $variables['elements']['content'] = array();
     // Test adding a class to the block content.
diff --git a/core/modules/comment/lib/Drupal/comment/Plugin/Action/UnpublishByKeywordComment.php b/core/modules/comment/lib/Drupal/comment/Plugin/Action/UnpublishByKeywordComment.php
index d123cfc..d669db4 100644
--- a/core/modules/comment/lib/Drupal/comment/Plugin/Action/UnpublishByKeywordComment.php
+++ b/core/modules/comment/lib/Drupal/comment/Plugin/Action/UnpublishByKeywordComment.php
@@ -49,7 +49,7 @@ protected function getDefaultConfiguration() {
   /**
    * {@inheritdoc}
    */
-  public function form(array $form, array &$form_state) {
+  public function buildConfigurationForm(array $form, array &$form_state) {
     $form['keywords'] = array(
       '#title' => t('Keywords'),
       '#type' => 'textarea',
@@ -62,7 +62,7 @@ public function form(array $form, array &$form_state) {
   /**
    * {@inheritdoc}
    */
-  public function submit(array &$form, array &$form_state) {
+  public function submitConfigurationForm(array &$form, array &$form_state) {
     $this->configuration['keywords'] = drupal_explode_tags($form_state['values']['keywords']);
   }
 
diff --git a/core/modules/node/lib/Drupal/node/Plugin/Action/AssignOwnerNode.php b/core/modules/node/lib/Drupal/node/Plugin/Action/AssignOwnerNode.php
index 76bc6d6..59255e2 100644
--- a/core/modules/node/lib/Drupal/node/Plugin/Action/AssignOwnerNode.php
+++ b/core/modules/node/lib/Drupal/node/Plugin/Action/AssignOwnerNode.php
@@ -79,7 +79,7 @@ protected function getDefaultConfiguration() {
   /**
    * {@inheritdoc}
    */
-  public function form(array $form, array &$form_state) {
+  public function buildConfigurationForm(array $form, array &$form_state) {
     $description = t('The username of the user to which you would like to assign ownership.');
     $count = $this->connection->query("SELECT COUNT(*) FROM {users}")->fetchField();
     $owner_name = '';
@@ -119,7 +119,7 @@ public function form(array $form, array &$form_state) {
   /**
    * {@inheritdoc}
    */
-  public function validate(array &$form, array &$form_state) {
+  public function validateConfigurationForm(array &$form, array &$form_state) {
     $exists = (bool) $this->connection->queryRange('SELECT 1 FROM {users} WHERE name = :name', 0, 1, array(':name' => $form_state['values']['owner_name']))->fetchField();
     if (!$exists) {
       form_set_error('owner_name', t('Enter a valid username.'));
@@ -129,7 +129,7 @@ public function validate(array &$form, array &$form_state) {
   /**
    * {@inheritdoc}
    */
-  public function submit(array &$form, array &$form_state) {
+  public function submitConfigurationForm(array &$form, array &$form_state) {
     $this->configuration['owner_uid'] = $this->connection->query('SELECT uid from {users} WHERE name = :name', array(':name' => $form_state['values']['owner_name']))->fetchField();
   }
 
diff --git a/core/modules/node/lib/Drupal/node/Plugin/Action/UnpublishByKeywordNode.php b/core/modules/node/lib/Drupal/node/Plugin/Action/UnpublishByKeywordNode.php
index 2d0f4ed..2ad65f8 100644
--- a/core/modules/node/lib/Drupal/node/Plugin/Action/UnpublishByKeywordNode.php
+++ b/core/modules/node/lib/Drupal/node/Plugin/Action/UnpublishByKeywordNode.php
@@ -48,7 +48,7 @@ protected function getDefaultConfiguration() {
   /**
    * {@inheritdoc}
    */
-  public function form(array $form, array &$form_state) {
+  public function buildConfigurationForm(array $form, array &$form_state) {
     $form['keywords'] = array(
       '#title' => t('Keywords'),
       '#type' => 'textarea',
@@ -61,7 +61,7 @@ public function form(array $form, array &$form_state) {
   /**
    * {@inheritdoc}
    */
-  public function submit(array &$form, array &$form_state) {
+  public function submitConfigurationForm(array &$form, array &$form_state) {
     $this->configuration['keywords'] = drupal_explode_tags($form_state['values']['keywords']);
   }
 
diff --git a/core/modules/system/lib/Drupal/system/Plugin/Core/Entity/Action.php b/core/modules/system/lib/Drupal/system/Plugin/Core/Entity/Action.php
index fe8f537..d50b68e 100644
--- a/core/modules/system/lib/Drupal/system/Plugin/Core/Entity/Action.php
+++ b/core/modules/system/lib/Drupal/system/Plugin/Core/Entity/Action.php
@@ -11,9 +11,9 @@
 use Drupal\Core\Entity\Annotation\EntityType;
 use Drupal\Core\Annotation\Translation;
 use Drupal\Core\Entity\EntityStorageControllerInterface;
+use Drupal\Core\Plugin\DefaultSinglePluginBag;
 use Drupal\system\ActionConfigEntityInterface;
-use Drupal\Core\Action\ActionBag;
-use Drupal\Core\Action\ConfigurableActionInterface;
+use Drupal\Core\Plugin\ConfigurablePluginInterface;
 
 /**
  * Defines the configured action entity.
@@ -81,7 +81,7 @@ class Action extends ConfigEntityBase implements ActionConfigEntityInterface {
   /**
    * The plugin bag that stores action plugins.
    *
-   * @var \Drupal\Core\Action\ActionBag
+   * @var \Drupal\Core\Plugin\DefaultSinglePluginBag
    */
   protected $pluginBag;
 
@@ -91,7 +91,7 @@ class Action extends ConfigEntityBase implements ActionConfigEntityInterface {
   public function __construct(array $values, $entity_type) {
     parent::__construct($values, $entity_type);
 
-    $this->pluginBag = new ActionBag(\Drupal::service('plugin.manager.action'), array($this->plugin), $this->configuration);
+    $this->pluginBag = new DefaultSinglePluginBag(\Drupal::service('plugin.manager.action'), array($this->plugin), $this->configuration);
   }
 
   /**
@@ -127,7 +127,7 @@ public function execute(array $entities) {
    * {@inheritdoc}
    */
   public function isConfigurable() {
-    return $this->getPlugin() instanceof ConfigurableActionInterface;
+    return $this->getPlugin() instanceof ConfigurablePluginInterface;
   }
 
   /**
@@ -184,7 +184,7 @@ public function getExportProperties() {
   public function preSave(EntityStorageControllerInterface $storage_controller) {
     $plugin = $this->getPlugin();
     // If this plugin has any configuration, ensure that it is set.
-    if ($plugin instanceof ConfigurableActionInterface) {
+    if ($plugin instanceof ConfigurablePluginInterface) {
       $this->set('configuration', $plugin->getConfiguration());
     }
   }
diff --git a/core/modules/user/lib/Drupal/user/Plugin/Action/ChangeUserRoleBase.php b/core/modules/user/lib/Drupal/user/Plugin/Action/ChangeUserRoleBase.php
index 9dfb056..079f066 100644
--- a/core/modules/user/lib/Drupal/user/Plugin/Action/ChangeUserRoleBase.php
+++ b/core/modules/user/lib/Drupal/user/Plugin/Action/ChangeUserRoleBase.php
@@ -26,7 +26,7 @@ protected function getDefaultConfiguration() {
   /**
    * {@inheritdoc}
    */
-  public function form(array $form, array &$form_state) {
+  public function buildConfigurationForm(array $form, array &$form_state) {
     $roles = user_role_names(TRUE);
     unset($roles[DRUPAL_AUTHENTICATED_RID]);
     $form['rid'] = array(
@@ -42,7 +42,7 @@ public function form(array $form, array &$form_state) {
   /**
    * {@inheritdoc}
    */
-  public function submit(array &$form, array &$form_state) {
+  public function submitConfigurationForm(array &$form, array &$form_state) {
     $this->configuration['rid'] = $form_state['values']['rid'];
   }
 
diff --git a/core/modules/views/lib/Drupal/views/Plugin/Block/ViewsBlock.php b/core/modules/views/lib/Drupal/views/Plugin/Block/ViewsBlock.php
index 8a0c919..d36f2bf 100644
--- a/core/modules/views/lib/Drupal/views/Plugin/Block/ViewsBlock.php
+++ b/core/modules/views/lib/Drupal/views/Plugin/Block/ViewsBlock.php
@@ -61,8 +61,8 @@ public function access() {
   /**
    * Overrides \Drupal\block\BlockBase::form().
    */
-  public function form($form, &$form_state) {
-    $form = parent::form($form, $form_state);
+  public function buildConfigurationForm(array $form, array &$form_state) {
+    $form = parent::buildConfigurationForm($form, $form_state);
 
     // Set the default label to '' so the views internal title is used.
     $form['label']['#default_value'] = '';