diff --git a/core/lib/Drupal/Core/Template/TwigEnvironment.php b/core/lib/Drupal/Core/Template/TwigEnvironment.php
index 2ac1d9d..62f320b 100644
--- a/core/lib/Drupal/Core/Template/TwigEnvironment.php
+++ b/core/lib/Drupal/Core/Template/TwigEnvironment.php
@@ -36,6 +36,19 @@ public function __construct(\Twig_LoaderInterface $loader = NULL, $options = arr
     // @todo Pass as arguments from the DIC.
     $this->cache_object = cache();
 
+    // Set twig path namespace for themes and modules
+    $namespaces = \Drupal::moduleHandler()->getModuleList();
+    foreach (\Drupal::service('theme_handler')->listInfo() as $theme => $info) {
+      $namespaces[$theme] = $info->filename;
+    }
+
+    foreach ($namespaces as $name => $filename) {
+      $templatesDirectory = dirname($filename) . '/templates';
+      if (file_exists($templatesDirectory)) {
+        $loader->addPath($templatesDirectory, $name);
+      }
+    }
+
     $this->templateClasses = array();
 
     parent::__construct($loader, $options);
diff --git a/core/modules/system/lib/Drupal/system/Tests/Theme/TwigNamespaceTest.php b/core/modules/system/lib/Drupal/system/Tests/Theme/TwigNamespaceTest.php
new file mode 100644
index 0000000..1068a3f
--- /dev/null
+++ b/core/modules/system/lib/Drupal/system/Tests/Theme/TwigNamespaceTest.php
@@ -0,0 +1,66 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\system\Tests\Theme\TwigNamespaceTest.
+ */
+
+namespace Drupal\system\Tests\Theme;
+
+use Drupal\simpletest\WebTestBase;
+
+/**
+ * Tests Twig namespaces.
+ */
+class TwigNamespaceTest extends WebTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  public static $modules = array('twig_theme_test', 'twig_namespace_a', 'twig_namespace_b', 'node');
+
+  /**
+   * @var \Drupal\Core\Template\TwigEnvironment
+   */
+  protected $twig;
+
+  public static function getInfo() {
+    return array(
+      'name' => 'Twig Namespaces',
+      'description' => 'Tests Twig namespaces.',
+      'group' => 'Theme',
+    );
+  }
+
+  function setUp() {
+    parent::setUp();
+    theme_enable(array('test_theme', 'bartik'));
+    $this->twig = \Drupal::service('twig');
+  }
+
+  /**
+   * Check to see if a value is a twig template.
+   */
+  public function assertTwigTemplate($value, $message = '', $group = 'Other') {
+    $this->assertTrue($value instanceof \Twig_Template, $message, $group);
+  }
+
+  public function testTemplateDiscovery() {
+    // Enabled module
+    $this->assertTwigTemplate($this->twig->resolveTemplate('@node/node.html.twig'), 'Found node.tpl.php in node module.');
+
+    // Enabled theme
+    $this->assertTwigTemplate($this->twig->resolveTemplate('@bartik/page.html.twig'), 'Found page.html.twig in bartik theme.');
+  }
+
+  public function testTwigNamespaces() {
+    // Test twig @extends and @include in template files.
+    $this->drupalSetContent(theme('twig_namespace_test'));
+
+    $this->assertText('This line is from twig_namespace_a/templates/test.html.twig');
+    $this->assertText('This line is from twig_namespace_b/templates/test.html.twig');
+  }
+
+}
diff --git a/core/modules/system/tests/modules/twig_theme_test/modules/twig_namespace_a/templates/test.html.twig b/core/modules/system/tests/modules/twig_theme_test/modules/twig_namespace_a/templates/test.html.twig
new file mode 100644
index 0000000..ed52e5e
--- /dev/null
+++ b/core/modules/system/tests/modules/twig_theme_test/modules/twig_namespace_a/templates/test.html.twig
@@ -0,0 +1,5 @@
+This line is from twig_namespace_a/templates/test.html.twig
+
+{% block content  %}
+This text is in a block.
+{% endblock %}
diff --git a/core/modules/system/tests/modules/twig_theme_test/modules/twig_namespace_a/twig_namespace_a.info.yml b/core/modules/system/tests/modules/twig_theme_test/modules/twig_namespace_a/twig_namespace_a.info.yml
new file mode 100644
index 0000000..d007f21
--- /dev/null
+++ b/core/modules/system/tests/modules/twig_theme_test/modules/twig_namespace_a/twig_namespace_a.info.yml
@@ -0,0 +1,7 @@
+name: 'Twig namespace test: Module A'
+type: module
+description: 'Support module for Twig namespace testing.'
+package: Testing
+version: VERSION
+core: 8.x
+hidden: true
diff --git a/core/modules/system/tests/modules/twig_theme_test/modules/twig_namespace_a/twig_namespace_a.module b/core/modules/system/tests/modules/twig_theme_test/modules/twig_namespace_a/twig_namespace_a.module
new file mode 100644
index 0000000..37a5536
--- /dev/null
+++ b/core/modules/system/tests/modules/twig_theme_test/modules/twig_namespace_a/twig_namespace_a.module
@@ -0,0 +1,6 @@
+<?php
+
+/**
+ * @file
+ * twig_namespace_a.module
+ */
diff --git a/core/modules/system/tests/modules/twig_theme_test/modules/twig_namespace_b/templates/test.html.twig b/core/modules/system/tests/modules/twig_theme_test/modules/twig_namespace_b/templates/test.html.twig
new file mode 100644
index 0000000..0c6f7f1
--- /dev/null
+++ b/core/modules/system/tests/modules/twig_theme_test/modules/twig_namespace_b/templates/test.html.twig
@@ -0,0 +1 @@
+This line is from twig_namespace_b/templates/test.html.twig
diff --git a/core/modules/system/tests/modules/twig_theme_test/modules/twig_namespace_b/twig_namespace_b.info.yml b/core/modules/system/tests/modules/twig_theme_test/modules/twig_namespace_b/twig_namespace_b.info.yml
new file mode 100644
index 0000000..d007f21
--- /dev/null
+++ b/core/modules/system/tests/modules/twig_theme_test/modules/twig_namespace_b/twig_namespace_b.info.yml
@@ -0,0 +1,7 @@
+name: 'Twig namespace test: Module A'
+type: module
+description: 'Support module for Twig namespace testing.'
+package: Testing
+version: VERSION
+core: 8.x
+hidden: true
diff --git a/core/modules/system/tests/modules/twig_theme_test/modules/twig_namespace_b/twig_namespace_b.module b/core/modules/system/tests/modules/twig_theme_test/modules/twig_namespace_b/twig_namespace_b.module
new file mode 100644
index 0000000..03d8ef7
--- /dev/null
+++ b/core/modules/system/tests/modules/twig_theme_test/modules/twig_namespace_b/twig_namespace_b.module
@@ -0,0 +1,6 @@
+<?php
+
+/**
+ * @file
+ * twig_namespace_b.module
+ */
diff --git a/core/modules/system/tests/modules/twig_theme_test/templates/twig_namespace_test.html.twig b/core/modules/system/tests/modules/twig_theme_test/templates/twig_namespace_test.html.twig
new file mode 100644
index 0000000..ea9a806
--- /dev/null
+++ b/core/modules/system/tests/modules/twig_theme_test/templates/twig_namespace_test.html.twig
@@ -0,0 +1,5 @@
+{% extends "@twig_namespace_a/test.html.twig" %}
+
+{% block content  %}
+  {% include "@twig_namespace_b/test.html.twig" %}
+{% endblock %}
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 934d1b0..6edb6f6 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
@@ -11,6 +11,10 @@ function twig_theme_test_theme($existing, $type, $theme, $path) {
     'variables' => array(),
     'template' => 'twig_theme_test.trans',
   );
+  $items['twig_namespace_test'] = array(
+    'variables' => array(),
+    'template' => 'twig_namespace_test',
+  );
   return $items;
 }