diff --git a/core/lib/Drupal/Component/Annotation/AnnotationInterface.php b/core/lib/Drupal/Component/Annotation/AnnotationInterface.php
index 6e577c2..a0dd75d 100644
--- a/core/lib/Drupal/Component/Annotation/AnnotationInterface.php
+++ b/core/lib/Drupal/Component/Annotation/AnnotationInterface.php
@@ -18,35 +18,35 @@
   public function get();
 
   /**
-   * @todo.
+   * Returns the name of the provider of the plugin.
    *
    * @return string
    */
   public function getProvider();
 
   /**
-   * @todo.
+   * Sets the name of the provider of the plugin.
    *
    * @param string $provider
    */
   public function setProvider($provider);
 
   /**
-   * @todo.
+   * Returns the unique ID for this plugin.
    *
    * @return string
    */
   public function getId();
 
   /**
-   * @todo.
+   * Returns the class of the plugin.
    *
    * @return string
    */
   public function getClass();
 
   /**
-   * @todo.
+   * Sets the class of the plugin.
    *
    * @param string $class
    */
diff --git a/core/lib/Drupal/Core/Entity/Annotation/EntityType.php b/core/lib/Drupal/Core/Entity/Annotation/EntityType.php
index 2a3639e..37d81b8 100644
--- a/core/lib/Drupal/Core/Entity/Annotation/EntityType.php
+++ b/core/lib/Drupal/Core/Entity/Annotation/EntityType.php
@@ -18,7 +18,8 @@
 class EntityType extends Plugin {
 
   /**
-   * @todo content_translation_entity_info_alter() uses this but it is undocumented.
+   * @todo content_translation_entity_info_alter() uses this but it is
+   *   undocumented. Fix in https://drupal.org/node/1968970.
    *
    * @var array
    */
diff --git a/core/lib/Drupal/Core/Entity/EntityManager.php b/core/lib/Drupal/Core/Entity/EntityManager.php
index 228492e..50b831d 100644
--- a/core/lib/Drupal/Core/Entity/EntityManager.php
+++ b/core/lib/Drupal/Core/Entity/EntityManager.php
@@ -491,4 +491,18 @@ public function getTranslationFromContext(EntityInterface $entity, $langcode = N
     return $translation;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function getDefinition($entity_type_name) {
+    return parent::getDefinition($entity_type_name);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDefinitions() {
+    return parent::getDefinitions();
+  }
+
 }
diff --git a/core/lib/Drupal/Core/Entity/EntityManagerInterface.php b/core/lib/Drupal/Core/Entity/EntityManagerInterface.php
index 6597326..cb962e0 100644
--- a/core/lib/Drupal/Core/Entity/EntityManagerInterface.php
+++ b/core/lib/Drupal/Core/Entity/EntityManagerInterface.php
@@ -263,14 +263,21 @@ public function getBundleInfo($entity_type);
   public function getTranslationFromContext(EntityInterface $entity, $langcode = NULL, $context = array());
 
   /**
-   * {@inheritdoc}
+   * Returns the entity type info for a specific entity type.
+   *
+   * @param string $entity_type_name
+   *   The name of the entity type.
    *
    * @return \Drupal\Core\Entity\EntityTypeInterface|null
+   *   Either the entity type object, or NULL if the name does not exist.
    */
-  public function getDefinition($plugin_id);
+  public function getDefinition($entity_type_name);
 
   /**
+   * Returns an array of entity type info, keyed by entity type name.
+   *
    * @return \Drupal\Core\Entity\EntityTypeInterface[]
+   *   An array of entity type objects.
    */
   public function getDefinitions();
 
diff --git a/core/lib/Drupal/Core/Entity/EntityType.php b/core/lib/Drupal/Core/Entity/EntityType.php
index 47e0780..d6c50eb 100644
--- a/core/lib/Drupal/Core/Entity/EntityType.php
+++ b/core/lib/Drupal/Core/Entity/EntityType.php
@@ -10,7 +10,7 @@
 use Drupal\Component\Utility\Unicode;
 
 /**
- * @todo.
+ * Provides an implementation of an entity type and its metadata.
  */
 class EntityType implements EntityTypeInterface {
 
@@ -43,14 +43,14 @@ class EntityType implements EntityTypeInterface {
   protected $entity_keys = array();
 
   /**
-   * @todo.
+   * The unique identifier of this entity type.
    *
    * @var string
    */
   protected $id;
 
   /**
-   * @todo.
+   * The name of the provider of this entity type.
    *
    * @var string
    */
@@ -145,28 +145,26 @@ class EntityType implements EntityTypeInterface {
   /**
    * The name of the entity type's base table.
    *
-   * @todo This is only used by \Drupal\Core\Entity\DatabaseStorageController.
-   *
    * @var string
    */
   protected $base_table;
 
   /**
-   * @todo.
+   * The name of the entity type's revision data table.
    *
    * @var string
    */
   protected $revision_data_table;
 
   /**
-   * @todo.
+   * The name of the entity type's revision table.
    *
    * @var string
    */
   protected $revision_table;
 
   /**
-   * @todo.
+   * The name of the entity type's data table.
    *
    * @var string
    */
@@ -180,7 +178,7 @@ class EntityType implements EntityTypeInterface {
   protected $translatable = FALSE;
 
   /**
-   * @todo.
+   * Returns the config prefix used by the configuration entity type.
    *
    * @var string
    */
@@ -194,7 +192,7 @@ class EntityType implements EntityTypeInterface {
   protected $label;
 
   /**
-   * @todo.
+   * A callable that can be used to provide the entity URI.
    *
    * @var callable
    */
diff --git a/core/lib/Drupal/Core/Entity/EntityTypeInterface.php b/core/lib/Drupal/Core/Entity/EntityTypeInterface.php
index 4d4c7b7..18405f5 100644
--- a/core/lib/Drupal/Core/Entity/EntityTypeInterface.php
+++ b/core/lib/Drupal/Core/Entity/EntityTypeInterface.php
@@ -8,7 +8,7 @@
 namespace Drupal\Core\Entity;
 
 /**
- * @todo.
+ * Provides an interface for an entity type and its metadata.
  */
 interface EntityTypeInterface {
 
@@ -47,18 +47,18 @@ public function set($key, $value);
   public function hasKey($key);
 
   /**
-   * @todo.
+   * Returns the unique identifier of the entity type.
    *
    * @return string
-   *   @todo.
+   *   The unique identifier of the entity type.
    */
   public function getId();
 
   /**
-   * @todo.
+   * Returns the name of the provider of this entity type.
    *
    * @return string
-   *   @todo.
+   *   The name of the provider of this entity type.
    */
   public function getProvider();
 
@@ -101,6 +101,8 @@ public function isRenderCacheable();
   /**
    * Indicates if the persistent cache of field data should be used.
    *
+   * @todo Used by FieldableEntityStorageControllerBase only.
+   *
    * The persistent cache should usually only be disabled if a higher level
    * persistent cache is available for the entity type.
    *
@@ -432,6 +434,8 @@ public function getBundleLabel();
   /**
    * Returns the name of the entity's base table.
    *
+   * @todo Used by DatabaseStorageController only.
+   *
    * @return string|bool
    *   The name of the entity's base table, or FALSE if none exists.
    */
@@ -448,66 +452,77 @@ public function getBaseTable();
   public function isTranslatable();
 
   /**
-   * @todo.
+   * Returns the config prefix used by the configuration entity type.
+   *
+   * @todo Used for configuration entities only.
    *
    * @return string|bool
-   *   @todo.
+   *   The config prefix, or FALSE if not a configuration entity type.
    */
   public function getConfigPrefix();
 
   /**
-   * @todo.
+   * Returns the name of the entity's revision data table.
+   *
+   * @todo Used by FieldableDatabaseStorageController only.
    *
    * @return string|bool
-   *   @todo.
+   *   The name of the entity type's revision data table.
    */
   public function getRevisionDataTable();
 
   /**
-   * @todo.
+   * Returns the name of the entity's revision table.
+   *
+   * @todo Used by FieldableDatabaseStorageController only.
    *
    * @return string|bool
-   *   @todo.
+   *   The name of the entity type's revision table.
    */
   public function getRevisionTable();
 
   /**
-   * @todo.
+   * Returns the name of the entity's data table.
+   *
+   * @todo Used by FieldableDatabaseStorageController only.
    *
    * @return string|bool
-   *   @todo.
+   *   The name of the entity type's data table.
    */
   public function getDataTable();
 
   /**
-   * @todo.
+   * Returns the human-readable name of the entity type.
    *
    * @return string
-   *   @todo.
+   *   The human-readable name of the entity type.
    */
   public function getLabel();
 
   /**
-   * @todo.
+   * Returns the lowercase form of the human-readable entity type name.
    *
    * @return string
-   *   @todo.
+   *   The lowercase form of the human-readable entity type name.
    */
   public function getLowercaseLabel();
 
   /**
-   * @todo.
+   * Returns a callable that can be used to provide the entity URI.
+   *
+   * This is only called if there is no matching link template for the link
+   * relationship type, and there is no bundle-specific callback provided.
    *
    * @return callable|bool
-   *   @todo.
+   *   A valid callback that is passed the entity or FALSE if none is specified.
    */
   public function getUriCallback();
 
   /**
-   * @todo.
+   * Sets a callable to use to provide the entity URI.
    *
    * @param callable $callback
-   *   @todo.
+   *   A callback to use to provide a URI for the entity.
    *
    * @return static
    */