diff --git a/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php b/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php
index 18e0260..a370552 100644
--- a/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php
+++ b/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php
@@ -230,7 +230,7 @@ public function preSave(EntityStorageControllerInterface $storage_controller) {
       ->condition('uuid', $this->uuid())
       ->execute();
     $matched_entity = reset($matching_entities);
-    if (!empty($matched_entity) && ($matched_entity != $this->id())) {
+    if (!empty($matched_entity) && ($matched_entity != $this->id()) && $matched_entity != $this->getOriginalId()) {
       throw new ConfigDuplicateUUIDException(format_string('Attempt to save a configuration entity %id with UUID %uuid when this UUID is already used for %matched', array('%id' => $this->id(), '%uuid' => $this->uuid(), '%matched' => $matched_entity)));
     }
 
diff --git a/core/lib/Drupal/Core/Entity/KeyValueStore/KeyValueEntityStorage.php b/core/lib/Drupal/Core/Entity/KeyValueStore/KeyValueEntityStorage.php
index 0412a1f..a95aaef 100644
--- a/core/lib/Drupal/Core/Entity/KeyValueStore/KeyValueEntityStorage.php
+++ b/core/lib/Drupal/Core/Entity/KeyValueStore/KeyValueEntityStorage.php
@@ -10,6 +10,7 @@
 use Drupal\Component\Utility\String;
 use Drupal\Component\Uuid\UuidInterface;
 use Drupal\Core\Config\Entity\ConfigEntityInterface;
+use Drupal\Core\Entity\ContentEntityInterface;
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\EntityMalformedException;
 use Drupal\Core\Entity\EntityStorageControllerBase;
@@ -17,6 +18,7 @@
 use Drupal\Core\Entity\EntityTypeInterface;
 use Drupal\Core\KeyValueStore\KeyValueStoreInterface;
 use Drupal\Core\Language\LanguageManagerInterface;
+use Drupal\Core\TypedData\TypedDataInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Symfony\Component\Serializer\Normalizer\NormalizerInterface;
 
@@ -102,6 +104,21 @@ public function create(array $values = array()) {
     $values += array('langcode' => $this->languageManager->getDefaultLanguage()->id);
 
     $entity = new $entity_class($values, $this->entityTypeId);
+
+    // @todo This is handled by FieldableEntityStorageControllerBase, which
+    //   assumes ContentEntityInterface, which is awful :(
+    if ($entity instanceof ContentEntityInterface) {
+      foreach ($entity as $name => $field) {
+        if (isset($values[$name])) {
+          $entity->$name = $values[$name];
+        }
+        elseif (!array_key_exists($name, $values)) {
+          $entity->get($name)->applyDefaultValue();
+        }
+        unset($values[$name]);
+      }
+    }
+
     $entity->enforceIsNew();
 
     // Assign a new UUID if there is none yet.
@@ -194,30 +211,69 @@ public function save(EntityInterface $entity) {
     if ($id === NULL || $id === '') {
       throw new EntityMalformedException('The entity does not have an ID.');
     }
+
+    // If this entity has a concept of 'original ID', use that.
+    if ($entity instanceof ConfigEntityInterface && $entity->getOriginalId() !== NULL) {
+      $id = $entity->getOriginalId();
+    }
+
+    // Track if this entity is new.
+    $is_new = $entity->isNew();
+    // Track if this entity exists already.
+    $id_exists = $this->keyValue->has($id);
+
+    // A new entity should not already exist.
+    if ($id_exists && $is_new) {
+      throw new EntityStorageException(String::format('@type entity with ID @id already exists.', array('@type' => $this->entityTypeId, '@id' => $id)));
+    }
+
+    // Load the original entity, if any.
+    if ($id_exists && !isset($entity->original)) {
+      $entity->original = $this->loadUnchanged($id);
+    }
+
+    // If this is a rename, delete the original entity.
+    if ($id_exists && $id !== $entity->id()) {
+      $this->keyValue->delete($entity->original->id());
+    }
+
+    // Allow code to run before saving.
     $entity->preSave($this);
     $this->invokeHook('presave', $entity);
 
-    $hook = !$entity->isNew() ? 'update' : 'insert';
-
     // Prefer the entity normalizer.
     // @todo Always use normalization after https://drupal.org/node/2216569.
     if ($this->normalizer) {
       $data = $this->normalizer->normalize($entity);
     }
-    // We know how to handle ConfigEntity.
     elseif ($entity instanceof ConfigEntityInterface) {
       $data = $entity->getExportProperties();
     }
+    elseif ($entity instanceof ContentEntityInterface) {
+      $data = $entity->getPropertyValues();
+    }
     else {
       throw new EntityStorageException(String::format('Cannot normalize entity of type @entity_type, enable the serialization module.', array('@entity_type' => $this->getEntityTypeId())));
     }
 
+    // Save the entity data in the key value store.
     $this->keyValue->set($entity->id(), $data);
+
+    // The entity is no longer new.
     $entity->enforceIsNew(FALSE);
-    $entity->postSave($this, FALSE);
-    $this->invokeHook($hook, $entity);
 
-    return $hook == 'update' ? SAVED_UPDATED : SAVED_NEW;
+    // Allow code to run after saving.
+    $entity->postSave($this, !$is_new);
+    $this->invokeHook($is_new ? 'insert' : 'update', $entity);
+
+    // If this entity has a concept of 'original ID', update it.
+    if ($id_exists && $entity instanceof ConfigEntityInterface) {
+      $entity->setOriginalId($entity->id());
+    }
+
+    unset($entity->original);
+
+    return $is_new ? SAVED_NEW : SAVED_UPDATED;
   }
 
   /**
diff --git a/core/modules/system/lib/Drupal/system/Tests/KeyValueStore/KeyValueConfigEntityStorageTest.php b/core/modules/system/lib/Drupal/system/Tests/KeyValueStore/KeyValueConfigEntityStorageTest.php
new file mode 100644
index 0000000..a814c50
--- /dev/null
+++ b/core/modules/system/lib/Drupal/system/Tests/KeyValueStore/KeyValueConfigEntityStorageTest.php
@@ -0,0 +1,35 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\system\Tests\KeyValueStore\KeyValueConfigEntityStorageTest.
+ */
+
+namespace Drupal\system\Tests\KeyValueStore;
+
+use Drupal\config\Tests\ConfigEntityTest;
+
+/**
+ * Tests config entity CRUD with key value entity storage.
+ */
+class KeyValueConfigEntityStorageTest extends ConfigEntityTest {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  public static $modules = array('keyvalue_test');
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getInfo() {
+    return array(
+      'name' => 'KeyValueEntityStorage config entity test',
+      'description' => 'Tests KeyValueEntityStorage for config entities.',
+      'group' => 'Entity API',
+    );
+  }
+
+}
diff --git a/core/modules/system/lib/Drupal/system/Tests/KeyValueStore/KeyValueContentEntityStorageTest.php b/core/modules/system/lib/Drupal/system/Tests/KeyValueStore/KeyValueContentEntityStorageTest.php
new file mode 100644
index 0000000..726deac
--- /dev/null
+++ b/core/modules/system/lib/Drupal/system/Tests/KeyValueStore/KeyValueContentEntityStorageTest.php
@@ -0,0 +1,164 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\system\Tests\KeyValueStore\KeyValueContentEntityStorageTest.
+ */
+
+namespace Drupal\system\Tests\KeyValueStore;
+
+use Drupal\Core\Entity\EntityMalformedException;
+use Drupal\Core\Entity\EntityStorageException;
+use Drupal\simpletest\WebTestBase;
+
+/**
+ * Tests content entity CRUD with key value entity storage.
+ */
+class KeyValueContentEntityStorageTest extends WebTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  public static $modules = array('keyvalue_test');
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getInfo() {
+    return array(
+      'name' => 'KeyValueEntityStorage content entity test',
+      'description' => 'Tests KeyValueEntityStorage for content entities.',
+      'group' => 'Entity API',
+    );
+  }
+
+  /**
+   * Tests CRUD operations.
+   */
+  function testCRUD() {
+    $default_langcode = language_default()->id;
+    // Verify default properties on a newly created empty entity.
+    $empty = entity_create('entity_test_label');
+    $this->assertIdentical($empty->id->value, NULL);
+    $this->assertIdentical($empty->name->value, NULL);
+    $this->assertTrue($empty->uuid->value);
+    $this->assertIdentical($empty->langcode->value, $default_langcode);
+
+    // Verify ConfigEntity properties/methods on the newly created empty entity.
+    $this->assertIdentical($empty->isNew(), TRUE);
+    $this->assertIdentical($empty->bundle(), 'entity_test_label');
+    $this->assertIdentical($empty->id(), NULL);
+    $this->assertTrue($empty->uuid());
+    $this->assertIdentical($empty->label(), NULL);
+
+    // Verify Entity properties/methods on the newly created empty entity.
+    $this->assertIdentical($empty->getEntityTypeId(), 'entity_test_label');
+    // The URI can only be checked after saving.
+    try {
+      $empty->urlInfo();
+      $this->fail('EntityMalformedException was thrown.');
+    }
+    catch (EntityMalformedException $e) {
+      $this->pass('EntityMalformedException was thrown.');
+    }
+
+    // Verify that an empty entity cannot be saved.
+    try {
+      $empty->save();
+      $this->fail('EntityMalformedException was thrown.');
+    }
+    catch (EntityMalformedException $e) {
+      $this->pass('EntityMalformedException was thrown.');
+    }
+
+    // Verify that an entity with an empty ID string is considered empty, too.
+    $empty_id = entity_create('entity_test_label', array(
+      'id' => '',
+    ));
+    $this->assertIdentical($empty_id->isNew(), TRUE);
+    try {
+      $empty_id->save();
+      $this->fail('EntityMalformedException was thrown.');
+    }
+    catch (EntityMalformedException $e) {
+      $this->pass('EntityMalformedException was thrown.');
+    }
+
+    // Verify properties on a newly created entity.
+    $entity_test = entity_create('entity_test_label', $expected = array(
+      'id' => $this->randomName(),
+      'name' => $this->randomString(),
+    ));
+    $this->assertIdentical($entity_test->id->value, $expected['id']);
+    $this->assertTrue($entity_test->uuid->value);
+    $this->assertNotEqual($entity_test->uuid->value, $empty->uuid->value);
+    $this->assertIdentical($entity_test->name->value, $expected['name']);
+    $this->assertIdentical($entity_test->langcode->value, $default_langcode);
+
+    // Verify methods on the newly created entity.
+    $this->assertIdentical($entity_test->isNew(), TRUE);
+    $this->assertIdentical($entity_test->id(), $expected['id']);
+    $this->assertTrue($entity_test->uuid());
+    $expected['uuid'] = $entity_test->uuid();
+    $this->assertIdentical($entity_test->label(), $expected['name']);
+
+    // Verify that the entity can be saved.
+    try {
+      $status = $entity_test->save();
+      $this->pass('EntityMalformedException was not thrown.');
+    }
+    catch (EntityMalformedException $e) {
+      $this->fail('EntityMalformedException was not thrown.');
+    }
+
+    // Verify that the correct status is returned and properties did not change.
+    $this->assertIdentical($status, SAVED_NEW);
+    $this->assertIdentical($entity_test->id(), $expected['id']);
+    $this->assertIdentical($entity_test->uuid(), $expected['uuid']);
+    $this->assertIdentical($entity_test->label(), $expected['name']);
+    $this->assertIdentical($entity_test->isNew(), FALSE);
+
+    // Save again, and verify correct status and properties again.
+    $status = $entity_test->save();
+    $this->assertIdentical($status, SAVED_UPDATED);
+    $this->assertIdentical($entity_test->id(), $expected['id']);
+    $this->assertIdentical($entity_test->uuid(), $expected['uuid']);
+    $this->assertIdentical($entity_test->label(), $expected['name']);
+    $this->assertIdentical($entity_test->isNew(), FALSE);
+
+    // Ensure that creating an entity with the same id as an existing one is not
+    // possible.
+    $same_id = entity_create('entity_test_label', array(
+      'id' => $entity_test->id(),
+    ));
+    $this->assertIdentical($same_id->isNew(), TRUE);
+    try {
+      $same_id->save();
+      $this->fail('Not possible to overwrite an entity entity.');
+    } catch (EntityStorageException $e) {
+      $this->pass('Not possible to overwrite an entity entity.');
+    }
+
+    // Verify that renaming the ID returns correct status and properties.
+    $ids = array($expected['id'], 'second_' . $this->randomName(4), 'third_' . $this->randomName(4));
+    for ($i = 1; $i < 3; $i++) {
+      $old_id = $ids[$i - 1];
+      $new_id = $ids[$i];
+      // Before renaming, everything should point to the current ID.
+      $this->assertIdentical($entity_test->id(), $old_id);
+
+      // Rename.
+      $entity_test->id = $new_id;
+      $this->assertIdentical($entity_test->id(), $new_id);
+      $status = $entity_test->save();
+      $this->assertIdentical($status, SAVED_UPDATED);
+      $this->assertIdentical($entity_test->isNew(), FALSE);
+
+      // Verify that originalID points to new ID directly after renaming.
+      $this->assertIdentical($entity_test->id(), $new_id);
+    }
+  }
+
+}
diff --git a/core/modules/system/tests/modules/keyvalue_test/keyvalue_test.info.yml b/core/modules/system/tests/modules/keyvalue_test/keyvalue_test.info.yml
new file mode 100644
index 0000000..41cfb33
--- /dev/null
+++ b/core/modules/system/tests/modules/keyvalue_test/keyvalue_test.info.yml
@@ -0,0 +1,10 @@
+name: 'KeyValue tests'
+type: module
+description: 'A support module to test key value storage.'
+core: 8.x
+package: Testing
+version: VERSION
+hidden: true
+dependencies:
+  - config_test
+  - entity_test
diff --git a/core/modules/system/tests/modules/keyvalue_test/keyvalue_test.module b/core/modules/system/tests/modules/keyvalue_test/keyvalue_test.module
new file mode 100644
index 0000000..96404a1
--- /dev/null
+++ b/core/modules/system/tests/modules/keyvalue_test/keyvalue_test.module
@@ -0,0 +1,19 @@
+<?php
+
+/**
+ * @file
+ * Sets up the key value entity storage.
+ */
+
+/**
+ * Implements hook_entity_type_alter().
+ */
+function keyvalue_test_entity_type_alter(array &$entity_types) {
+  /** @var $entity_types \Drupal\Core\Entity\EntityTypeInterface[] */
+  if (isset($entity_types['config_test'])) {
+    $entity_types['config_test']->setStorageClass('Drupal\Core\Entity\KeyValueStore\KeyValueEntityStorage');
+  }
+  if (isset($entity_types['entity_test_label'])) {
+    $entity_types['entity_test_label']->setStorageClass('Drupal\Core\Entity\KeyValueStore\KeyValueEntityStorage');
+  }
+}
diff --git a/core/tests/Drupal/Tests/Core/Entity/KeyValueStore/KeyValueEntityStorageTest.php b/core/tests/Drupal/Tests/Core/Entity/KeyValueStore/KeyValueEntityStorageTest.php
index c0fc209..e86b7f2 100644
--- a/core/tests/Drupal/Tests/Core/Entity/KeyValueStore/KeyValueEntityStorageTest.php
+++ b/core/tests/Drupal/Tests/Core/Entity/KeyValueStore/KeyValueEntityStorageTest.php
@@ -8,6 +8,7 @@
 namespace Drupal\Tests\Core\Entity\KeyValueStore {
 
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\ContentEntityInterface;
 use Drupal\Core\Language\Language;
 use Drupal\Tests\UnitTestCase;
 use Drupal\Core\Entity\KeyValueStore\KeyValueEntityStorage;
@@ -272,6 +273,26 @@ public function testSaveConfigEntityWithoutNormalizer() {
   }
 
   /**
+   * @covers ::save()
+   */
+  public function testSaveContentEntityWithoutNormalizer() {
+    $expected = array('id' => 'foo');
+    $this->entityStorage = new KeyValueEntityStorage($this->entityType, $this->keyValueStore, $this->uuidService, $this->languageManager);
+    $this->entityStorage->setModuleHandler($this->moduleHandler);
+    $this->keyValueStore->expects($this->once())
+      ->method('set')
+      ->with('foo', $expected);
+    $entity = $this->getMock('Drupal\Tests\Core\Entity\KeyValueStore\TestContentEntityInterface');
+    $entity->expects($this->atLeastOnce())
+      ->method('id')
+      ->will($this->returnValue('foo'));
+    $entity->expects($this->once())
+      ->method('getPropertyValues')
+      ->will($this->returnValue($expected));
+    $this->entityStorage->save($entity);
+  }
+
+  /**
    * @covers ::load()
    */
   public function testLoad() {
@@ -395,6 +416,14 @@ protected function getMockEntity($methods = array()) {
 
 }
 
+/**
+ * Provides a testable version of ContentEntityInterface.
+ *
+ * @see https://github.com/sebastianbergmann/phpunit-mock-objects/commit/96a6794
+ */
+interface TestContentEntityInterface extends \Iterator, ContentEntityInterface {
+}
+
 }
 namespace {
   if (!defined('SAVED_NEW')) {