diff --git a/core/core.services.yml b/core/core.services.yml
index 9c3f606..dfa82fa 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -1062,11 +1062,22 @@ services:
     class: Twig_Extension_Debug
     tags:
       - { name: twig.extension }
-  twig.loader:
-    alias: twig.loader.filesystem
+  twig.loader.chain:
+    class: Twig_Loader_Chain
   twig.loader.filesystem:
     class: Twig_Loader_Filesystem
     arguments: ['%app.root%']
+    tags:
+      - { name: twig.loader, priority: 100 }
+  twig.loader.theme_registry:
+    class: Drupal\Core\Template\TwigThemeRegistryLoader
+    arguments: ['@theme.registry']
+    tags:
+      - { name: twig.loader, priority: 0 }
+  twig.loader.string:
+    class: Twig_Loader_String
+    tags:
+      - { name: twig.loader, priority: -100 }
   element_info:
     alias: plugin.manager.element_info
   file.mime_type.guesser:
diff --git a/core/lib/Drupal/Core/CoreServiceProvider.php b/core/lib/Drupal/Core/CoreServiceProvider.php
index db54f91..cd2c93f 100644
--- a/core/lib/Drupal/Core/CoreServiceProvider.php
+++ b/core/lib/Drupal/Core/CoreServiceProvider.php
@@ -19,6 +19,7 @@
 use Drupal\Core\DependencyInjection\Compiler\RegisterKernelListenersPass;
 use Drupal\Core\DependencyInjection\Compiler\RegisterAccessChecksPass;
 use Drupal\Core\DependencyInjection\Compiler\RegisterServicesForDestructionPass;
+use Drupal\Core\DependencyInjection\Compiler\TwigLoaderPass;
 use Drupal\Core\Plugin\PluginManagerPass;
 use Symfony\Component\DependencyInjection\Compiler\PassConfig;
 
@@ -57,6 +58,7 @@ public function register(ContainerBuilder $container) {
     // Collect tagged handler services as method calls on consumer services.
     $container->addCompilerPass(new TaggedHandlersPass());
     $container->addCompilerPass(new RegisterStreamWrappersPass());
+    $container->addCompilerPass(new TwigLoaderPass());
 
     // Add a compiler pass for registering event subscribers.
     $container->addCompilerPass(new RegisterKernelListenersPass(), PassConfig::TYPE_AFTER_REMOVING);
diff --git a/core/lib/Drupal/Core/DependencyInjection/Compiler/TwigLoaderPass.php b/core/lib/Drupal/Core/DependencyInjection/Compiler/TwigLoaderPass.php
new file mode 100644
index 0000000..fee8ed4
--- /dev/null
+++ b/core/lib/Drupal/Core/DependencyInjection/Compiler/TwigLoaderPass.php
@@ -0,0 +1,62 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\DependencyInjection\Compiler\TwigLoaderPass.
+ */
+
+namespace Drupal\Core\DependencyInjection\Compiler;
+
+use Symfony\Component\DependencyInjection\Compiler\CompilerPassInterface;
+use Symfony\Component\DependencyInjection\ContainerBuilder;
+use Symfony\Component\DependencyInjection\Exception\LogicException;
+use Symfony\Component\DependencyInjection\Reference;
+
+/**
+ * Adds services tagged twig.loader as Twig loaders.
+ *
+ * This class is a copy of the TwigLoaderPass from Symfony.
+ * @link https://github.com/symfony/symfony/blob/master/src/Symfony/Bundle/TwigBundle/DependencyInjection/Compiler/TwigLoaderPass.php
+ */
+class TwigLoaderPass implements CompilerPassInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function process(ContainerBuilder $container) {
+    if (false === $container->hasDefinition('twig')) {
+      return;
+    }
+
+    // Register additional template loaders.
+    $loaderIds = $container->findTaggedServiceIds('twig.loader');
+
+    if (count($loaderIds) === 0) {
+      throw new LogicException('No twig loaders found. You need to tag at least one loader with "twig.loader"');
+    }
+
+    if (count($loaderIds) === 1) {
+      $container->setAlias('twig.loader', key($loaderIds));
+    }
+    else {
+      $chainLoader = $container->getDefinition('twig.loader.chain');
+      $loaders = [];
+      $priorities = [];
+
+      // Sort the loaders by priority. Lower priority loaders are loaded later.
+      foreach ($loaderIds as $id => $attributes) {
+        foreach ($attributes as $attribute) {
+          $priorities[$id] = isset($attribute['priority']) ? $attribute['priority'] : 0;
+        }
+        $loaders[$id] = $container->getDefinition($id);
+      }
+      array_multisort($priorities, SORT_DESC, $loaders);
+
+      foreach ($loaders as $id => $loader) {
+        $chainLoader->addMethodCall('addLoader', array(new Reference($id)));
+      }
+      $container->setAlias('twig.loader', 'twig.loader.chain');
+    }
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Template/TwigEnvironment.php b/core/lib/Drupal/Core/Template/TwigEnvironment.php
index 97341ac..184272d 100644
--- a/core/lib/Drupal/Core/Template/TwigEnvironment.php
+++ b/core/lib/Drupal/Core/Template/TwigEnvironment.php
@@ -54,7 +54,9 @@ public function __construct(\Twig_LoaderInterface $loader = NULL, ModuleHandlerI
     foreach ($namespaces as $name => $path) {
       $templatesDirectory = $path . '/templates';
       if (file_exists($templatesDirectory)) {
-        $loader->addPath($templatesDirectory, $name);
+        // @todo Inject this? Might be weird injecting two TwigLoaderInterface?
+        //   Or solve this another way.
+        \Drupal::service('twig.loader.filesystem')->addPath($templatesDirectory, $name);
       }
     }
 
@@ -69,7 +71,7 @@ public function __construct(\Twig_LoaderInterface $loader = NULL, ModuleHandlerI
     // Ensure autoescaping is always on.
     $options['autoescape'] = TRUE;
 
-    $this->loader = new \Twig_Loader_Chain([$loader, new \Twig_Loader_String()]);
+    $this->loader = $loader;
     parent::__construct($this->loader, $options);
   }
 
diff --git a/core/lib/Drupal/Core/Template/TwigThemeRegistryLoader.php b/core/lib/Drupal/Core/Template/TwigThemeRegistryLoader.php
new file mode 100644
index 0000000..86c0c9a
--- /dev/null
+++ b/core/lib/Drupal/Core/Template/TwigThemeRegistryLoader.php
@@ -0,0 +1,69 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Template\TwigThemeRegistryLoader.
+ */
+
+namespace Drupal\Core\Template;
+
+use Drupal\Core\Theme\Registry;
+
+/**
+ * Loads templates based on information from the Drupal theme registry.
+ *
+ * Allows for template inheritance based on the currently active template.
+ */
+class TwigThemeRegistryLoader extends \Twig_Loader_Filesystem {
+
+  /**
+   * The theme registry used to determine which template to use.
+   *
+   * @var \Drupal\Core\Theme\Registry
+   */
+  protected $themeRegistry;
+
+  /**
+   * Constructs a new TwigThemeRegistryLoader object.
+   *
+   * @param \Drupal\Core\Theme\Registry $theme_registry
+   *   The theme registry.
+   */
+  public function __construct(Registry $theme_registry) {
+    $this->themeRegistry = $theme_registry;
+  }
+
+  /**
+   * Finds the path to the requested template.
+   *
+   * @param string $name
+   *   The name of the template to load.
+   *
+   * @return string
+   *   The path to the template.
+   *
+   * @throws Twig_Error_Loader
+   *   Thrown if a template matching $name cannot be found.
+   */
+  protected function findTemplate($name) {
+    // Allow for loading based on the Drupal theme registry.
+    $hook = str_replace('.html.twig', '', strtr($name, '-', '_'));
+    $theme_registry = $this->themeRegistry->getRuntime();
+
+    if ($theme_registry->has($hook)) {
+      $info = $theme_registry->get($hook);
+      if (isset($info['path'])) {
+        $path = $info['path'] . '/' . $name;
+      }
+      elseif (isset($info['template'])) {
+        $path = $info['template'] . '.html.twig';
+      }
+      if (isset($path) && is_file($path)) {
+        return $this->cache[$name] = $path;
+      }
+    }
+
+    throw new \Twig_Error_Loader(sprintf('Unable to find template "%s" in the Drupal theme registry.', $name));
+  }
+
+}
diff --git a/core/modules/system/src/Tests/Theme/TwigLoaderTest.php b/core/modules/system/src/Tests/Theme/TwigLoaderTest.php
new file mode 100644
index 0000000..91de1e4
--- /dev/null
+++ b/core/modules/system/src/Tests/Theme/TwigLoaderTest.php
@@ -0,0 +1,39 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\system\Tests\Theme\TwigLoaderTest.
+ */
+
+namespace Drupal\system\Tests\Theme;
+
+use Drupal\simpletest\WebTestBase;
+
+/**
+ * Tests adding Twig loaders.
+ *
+ * @group Theme
+ */
+class TwigLoaderTest extends WebTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  public static $modules = ['twig_loader_test'];
+
+  /**
+   * Tests adding an additional twig loader to the loader chain.
+   */
+  public function testTwigLoaderAddition() {
+    $environment = \Drupal::service('twig');
+
+    $template = $environment->loadTemplate('kittens');
+    $this->assertEqual($template->render(array()), 'kittens', 'Passing "kittens" to the custom Twig loader returns "kittens".');
+
+    $template = $environment->loadTemplate('meow');
+    $this->assertEqual($template->render(array()), 'cats', 'Passing something other than "kittens" to the custom Twig loader returns "cats".');
+  }
+
+}
diff --git a/core/modules/system/src/Tests/Theme/TwigRegistryLoaderTest.php b/core/modules/system/src/Tests/Theme/TwigRegistryLoaderTest.php
new file mode 100644
index 0000000..431f2c1
--- /dev/null
+++ b/core/modules/system/src/Tests/Theme/TwigRegistryLoaderTest.php
@@ -0,0 +1,70 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\system\Tests\Theme\TwigRegistryLoaderTest.
+ */
+
+namespace Drupal\system\Tests\Theme;
+
+use Drupal\simpletest\WebTestBase;
+
+/**
+ * Tests Twig registry loader.
+ *
+ * @group Theme
+ */
+class TwigRegistryLoaderTest extends WebTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  public static $modules = array('twig_theme_test', 'block');
+
+  /**
+   * @var \Drupal\Core\Template\TwigEnvironment
+   */
+  protected $twig;
+
+  protected function setUp() {
+    parent::setUp();
+    \Drupal::service('theme_handler')->install(array('test_theme_twig_registry_loader'));
+    $this->twig = \Drupal::service('twig');
+  }
+
+  /**
+   * Checks to see if a value is a twig template.
+   */
+  public function assertTwigTemplate($value, $message = '', $group = 'Other') {
+    $this->assertTrue($value instanceof \Twig_Template, $message, $group);
+  }
+
+  /**
+   * Tests template discovery using the Drupal theme registry.
+   */
+  public function testTemplateDiscovery() {
+    $this->assertTwigTemplate($this->twig->resolveTemplate('block.html.twig'), 'Found block.html.twig in block module.');
+  }
+
+  /**
+   * Tests template extension and includes using the Drupal theme registry.
+   */
+  public function testTwigNamespaces() {
+    // Test the module-provided extend and insert templates.
+    $this->drupalGet('twig-theme-test/registry-loader');
+    $this->assertText('This line is from twig_theme_test/templates/twig_registry_loader_test_extend.html.twig');
+    $this->assertText('This line is from twig_theme_test/templates/twig_registry_loader_test_include.html.twig');
+
+    // Enable a theme that overrides the extend and insert templates to ensure
+    // they are picked up by the registry loader.
+    \Drupal::config('system.theme')
+      ->set('default', 'test_theme_twig_registry_loader')
+      ->save();
+    $this->drupalGet('twig-theme-test/registry-loader');
+    $this->assertText('This line is from test_theme_twig_registry_loader/templates/twig_registry_loader_test_extend.html.twig');
+    $this->assertText('This line is from test_theme_twig_registry_loader/templates/twig_registry_loader_test_include.html.twig');
+  }
+
+}
diff --git a/core/modules/system/templates/block--system-branding-block.html.twig b/core/modules/system/templates/block--system-branding-block.html.twig
index 4cf0f1a..f648773 100644
--- a/core/modules/system/templates/block--system-branding-block.html.twig
+++ b/core/modules/system/templates/block--system-branding-block.html.twig
@@ -1,4 +1,4 @@
-{% extends "@block/block.html.twig" %}
+{% extends "block.html.twig" %}
 {#
 /**
  * @file
diff --git a/core/modules/system/tests/modules/twig_loader_test/src/Loader/TestLoader.php b/core/modules/system/tests/modules/twig_loader_test/src/Loader/TestLoader.php
new file mode 100644
index 0000000..9f32969
--- /dev/null
+++ b/core/modules/system/tests/modules/twig_loader_test/src/Loader/TestLoader.php
@@ -0,0 +1,50 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\twig_loader_test\Loader\TestLoader.
+ */
+
+namespace Drupal\twig_loader_test\Loader;
+
+use Drupal\Core\Template\Loader;
+
+/**
+ * A test Twig loader.
+ */
+class TestLoader implements \Twig_LoaderInterface, \Twig_ExistsLoaderInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getSource($name) {
+    if ($name == 'kittens') {
+      return $name;
+    }
+    else {
+      return 'cats';
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function exists($name) {
+    return TRUE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheKey($name) {
+    return $name;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function isFresh($name, $time) {
+    return TRUE;
+  }
+
+}
diff --git a/core/modules/system/tests/modules/twig_loader_test/twig_loader_test.info.yml b/core/modules/system/tests/modules/twig_loader_test/twig_loader_test.info.yml
new file mode 100644
index 0000000..cf04aae
--- /dev/null
+++ b/core/modules/system/tests/modules/twig_loader_test/twig_loader_test.info.yml
@@ -0,0 +1,6 @@
+name: 'Twig Loader Test'
+type: module
+description: 'Support module for testing adding Twig loaders.'
+package: Testing
+version: VERSION
+core: 8.x
diff --git a/core/modules/system/tests/modules/twig_loader_test/twig_loader_test.services.yml b/core/modules/system/tests/modules/twig_loader_test/twig_loader_test.services.yml
new file mode 100644
index 0000000..1b19948
--- /dev/null
+++ b/core/modules/system/tests/modules/twig_loader_test/twig_loader_test.services.yml
@@ -0,0 +1,5 @@
+services:
+  twig_loader_test.twig.test_loader:
+    class: Drupal\twig_loader_test\Loader\TestLoader
+    tags:
+      - { name: twig.loader }
diff --git a/core/modules/system/tests/modules/twig_theme_test/src/TwigThemeTestController.php b/core/modules/system/tests/modules/twig_theme_test/src/TwigThemeTestController.php
index f657c4d..7009bc4 100644
--- a/core/modules/system/tests/modules/twig_theme_test/src/TwigThemeTestController.php
+++ b/core/modules/system/tests/modules/twig_theme_test/src/TwigThemeTestController.php
@@ -49,4 +49,11 @@ public function linkGeneratorRender() {
     );
   }
 
+  /**
+   * Menu callback for testing the Twig registry loader.
+   */
+  public function registryLoaderRender() {
+    return array('#theme' => 'twig_registry_loader_test');
+  }
+
 }
diff --git a/core/modules/system/tests/modules/twig_theme_test/templates/twig_registry_loader_test.html.twig b/core/modules/system/tests/modules/twig_theme_test/templates/twig_registry_loader_test.html.twig
new file mode 100644
index 0000000..8776f5e
--- /dev/null
+++ b/core/modules/system/tests/modules/twig_theme_test/templates/twig_registry_loader_test.html.twig
@@ -0,0 +1,5 @@
+{% extends "twig_registry_loader_test_extend.html.twig" %}
+
+{% block content %}
+  {% include "twig_registry_loader_test_include.html.twig" %}
+{% endblock %}
diff --git a/core/modules/system/tests/modules/twig_theme_test/templates/twig_registry_loader_test_extend.html.twig b/core/modules/system/tests/modules/twig_theme_test/templates/twig_registry_loader_test_extend.html.twig
new file mode 100644
index 0000000..a5a5af1
--- /dev/null
+++ b/core/modules/system/tests/modules/twig_theme_test/templates/twig_registry_loader_test_extend.html.twig
@@ -0,0 +1,5 @@
+This line is from twig_theme_test/templates/twig_registry_loader_test_extend.html.twig
+
+{% block content %}
+This text is in a block.
+{% endblock %}
diff --git a/core/modules/system/tests/modules/twig_theme_test/templates/twig_registry_loader_test_include.html.twig b/core/modules/system/tests/modules/twig_theme_test/templates/twig_registry_loader_test_include.html.twig
new file mode 100644
index 0000000..bb8c056
--- /dev/null
+++ b/core/modules/system/tests/modules/twig_theme_test/templates/twig_registry_loader_test_include.html.twig
@@ -0,0 +1 @@
+This line is from twig_theme_test/templates/twig_registry_loader_test_include.html.twig
diff --git a/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.module b/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.module
index b754ffa..ba850f7 100644
--- a/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.module
+++ b/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.module
@@ -19,6 +19,18 @@ function twig_theme_test_theme($existing, $type, $theme, $path) {
     'variables' => array(),
     'template' => 'twig_namespace_test',
   );
+  $items['twig_registry_loader_test'] = array(
+    'variables' => array(),
+    'template' => 'twig_registry_loader_test',
+  );
+  $items['twig_registry_loader_test_include'] = array(
+    'variables' => array(),
+    'template' => 'twig_registry_loader_test_include',
+  );
+  $items['twig_registry_loader_test_extend'] = array(
+    'variables' => array(),
+    'template' => 'twig_registry_loader_test_extend',
+  );
   $items['twig_raw_test'] = array(
     'variables' => array('script' => ''),
   );
diff --git a/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.routing.yml b/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.routing.yml
index d631898..d7c2f39 100644
--- a/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.routing.yml
+++ b/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.routing.yml
@@ -25,3 +25,10 @@ twig_theme_test_link_generator:
     _content: '\Drupal\twig_theme_test\TwigThemeTestController::linkGeneratorRender'
   requirements:
     _access: 'TRUE'
+
+twig_theme_test.registry_loader:
+  path: '/twig-theme-test/registry-loader'
+  defaults:
+    _content: '\Drupal\twig_theme_test\TwigThemeTestController::registryLoaderRender'
+  requirements:
+    _access: 'TRUE'
diff --git a/core/modules/system/tests/themes/test_theme_twig_registry_loader/templates/twig_registry_loader_test_extend.html.twig b/core/modules/system/tests/themes/test_theme_twig_registry_loader/templates/twig_registry_loader_test_extend.html.twig
new file mode 100644
index 0000000..7d5cb0e
--- /dev/null
+++ b/core/modules/system/tests/themes/test_theme_twig_registry_loader/templates/twig_registry_loader_test_extend.html.twig
@@ -0,0 +1,5 @@
+This line is from test_theme_twig_registry_loader/templates/twig_registry_loader_test_extend.html.twig
+
+{% block content %}
+This text is in a block.
+{% endblock %}
diff --git a/core/modules/system/tests/themes/test_theme_twig_registry_loader/templates/twig_registry_loader_test_include.html.twig b/core/modules/system/tests/themes/test_theme_twig_registry_loader/templates/twig_registry_loader_test_include.html.twig
new file mode 100644
index 0000000..7097adf
--- /dev/null
+++ b/core/modules/system/tests/themes/test_theme_twig_registry_loader/templates/twig_registry_loader_test_include.html.twig
@@ -0,0 +1 @@
+This line is from test_theme_twig_registry_loader/templates/twig_registry_loader_test_include.html.twig
diff --git a/core/modules/system/tests/themes/test_theme_twig_registry_loader/test_theme_twig_registry_loader.info.yml b/core/modules/system/tests/themes/test_theme_twig_registry_loader/test_theme_twig_registry_loader.info.yml
new file mode 100644
index 0000000..9ee01c5
--- /dev/null
+++ b/core/modules/system/tests/themes/test_theme_twig_registry_loader/test_theme_twig_registry_loader.info.yml
@@ -0,0 +1,5 @@
+name: 'Twig registry loader test'
+type: theme
+description: 'Support module for Twig registry loader testing.'
+version: VERSION
+core: 8.x
diff --git a/core/themes/bartik/templates/block--system-branding-block.html.twig b/core/themes/bartik/templates/block--system-branding-block.html.twig
index f6147a6..4a4b733 100644
--- a/core/themes/bartik/templates/block--system-branding-block.html.twig
+++ b/core/themes/bartik/templates/block--system-branding-block.html.twig
@@ -1,4 +1,4 @@
-{% extends "@block/block.html.twig" %}
+{% extends "block.html.twig" %}
 {#
 /**
  * @file