diff --git a/core/modules/comment/comment.module b/core/modules/comment/comment.module
index dfa156d..e62b710 100644
--- a/core/modules/comment/comment.module
+++ b/core/modules/comment/comment.module
@@ -1030,6 +1030,9 @@ function comment_build_content(Comment $comment, Node $node, $view_mode = 'full'
   // Remove previously built content, if exists.
   $comment->content = array();
 
+  // Allow modules to change the view mode.
+  drupal_alter('entity_view_mode', $view_mode, $comment, $langcode);
+
   // Build fields content.
   field_attach_prepare_view('comment', array($comment->cid => $comment), $view_mode, $langcode);
   entity_prepare_view('comment', array($comment->cid => $comment), $langcode);
diff --git a/core/modules/entity/entity.api.php b/core/modules/entity/entity.api.php
index 02d8754..c47ba55 100644
--- a/core/modules/entity/entity.api.php
+++ b/core/modules/entity/entity.api.php
@@ -434,3 +434,20 @@ function hook_entity_prepare_view($entities, $entity_type) {
     }
   }
 }
+
+/**
+ * Change the view mode of an entity that is being displayed.
+ *
+ * @param string $view_mode
+ *   The view_mode that is to be used to display the entity.
+ * @param Drupal\entity\EntityInterface $entity
+ *   The entity that is being viewed.
+ * @param string $langcode
+ *   The language code the entity is being displayed for.
+ */
+function hook_entity_view_mode_alter(&$view_mode, Drupal\entity\EntityInterface $entity, $langcode) {
+  // For nodes, change the view mode when it is teaser.
+  if ($entity->entityType() == 'node' && $view_mode == 'teaser') {
+    $view_mode = 'my_custom_view_mode';
+  }
+}
diff --git a/core/modules/node/lib/Drupal/node/Tests/NodeEntityViewModeAlterTest.php b/core/modules/node/lib/Drupal/node/Tests/NodeEntityViewModeAlterTest.php
new file mode 100644
index 0000000..fba3ffe
--- /dev/null
+++ b/core/modules/node/lib/Drupal/node/Tests/NodeEntityViewModeAlterTest.php
@@ -0,0 +1,53 @@
+<?php
+
+/**
+ * @file
+ * Definition of Drupal\node\Tests\NodeEntityViewModeAlterTest.
+ */
+
+namespace Drupal\node\Tests;
+
+/**
+ * Tests changing view modes for nodes.
+ */
+class NodeEntityViewModeAlterTest extends NodeTestBase {
+  public static function getInfo() {
+    return array(
+      'name' => 'Node entity view mode',
+      'description' => 'Test changing view mode.',
+      'group' => 'Node'
+    );
+  }
+
+  function setUp() {
+    // Enable dummy module that implements hook_node_view().
+    parent::setUp('node_test');
+
+    $web_user = $this->drupalCreateUser(array('create page content', 'edit own page content'));
+    $this->drupalLogin($web_user);
+  }
+
+  /**
+   * Create a "Basic page" node and verify its consistency in the database.
+   */
+  function testNodeViewModeChange() {
+    // Create a node.
+    $edit = array();
+    $langcode = LANGUAGE_NOT_SPECIFIED;
+    $edit["title"] = $this->randomName(8);
+    $edit["body[$langcode][0][value]"] = t('Data that should appear only in the body for the node.');
+    $edit["body[$langcode][0][summary]"] = t('Extra data that should appear only in the teaser for the node.');
+    $this->drupalPost('node/add/page', $edit, t('Save'));
+
+    $node = $this->drupalGetNodeByTitle($edit["title"]);
+
+    // Set the flag to alter the view mode and view the node.
+    variable_set('node_test_change_view_mode', 'teaser');
+    $this->drupalGet('node/' . $node->nid);
+
+    // Check that teaser mode is viewed.
+    $this->assertText('Extra data that should appear only in the teaser for the node.', 'Teaser text present');
+    // Make sure body text is not present.
+    $this->assertNoText('Data that should appear only in the body for the node.', 'Body text not present');
+  }
+}
diff --git a/core/modules/node/node.module b/core/modules/node/node.module
index 3d83cd4..f7ccdbf 100644
--- a/core/modules/node/node.module
+++ b/core/modules/node/node.module
@@ -1272,6 +1272,9 @@ function node_build_content(Node $node, $view_mode = 'full', $langcode = NULL) {
   // Remove previously built content, if exists.
   $node->content = array();
 
+  // Allow modules to change the view mode.
+  drupal_alter('entity_view_mode', $view_mode, $node, $langcode);
+
   // The 'view' hook can be implemented to overwrite the default function
   // to display nodes.
   if (node_hook($node, 'view')) {
diff --git a/core/modules/node/tests/modules/node_test/node_test.module b/core/modules/node/tests/modules/node_test/node_test.module
index f541d10..1b301c3 100644
--- a/core/modules/node/tests/modules/node_test/node_test.module
+++ b/core/modules/node/tests/modules/node_test/node_test.module
@@ -151,3 +151,13 @@ function node_test_node_update(Node $node) {
     }
   }
 }
+
+/**
+ * Implements hook_entity_view_mode_alter().
+ */
+function node_test_entity_view_mode_alter(&$view_mode, Drupal\entity\EntityInterface $entity, $langcode) {
+  // Only alter the view mode if we are on the test callback.
+  if ($change_view_mode = variable_get('node_test_change_view_mode', '')) {
+    $view_mode = $change_view_mode;
+  }
+}
diff --git a/core/modules/taxonomy/taxonomy.module b/core/modules/taxonomy/taxonomy.module
index 8aa78df..43374f3 100644
--- a/core/modules/taxonomy/taxonomy.module
+++ b/core/modules/taxonomy/taxonomy.module
@@ -588,6 +588,9 @@ function taxonomy_term_view(Term $term, $view_mode = 'full', $langcode = NULL) {
     $langcode = drupal_container()->get(LANGUAGE_TYPE_CONTENT)->langcode;
   }
 
+  // Allow modules to change the view mode.
+  drupal_alter('entity_view_mode', $view_mode, $term, $langcode);
+
   field_attach_prepare_view('taxonomy_term', array($term->tid => $term), $view_mode, $langcode);
   entity_prepare_view('taxonomy_term', array($term->tid => $term), $langcode);
 
diff --git a/core/modules/user/user.module b/core/modules/user/user.module
index e373062..591fca1 100644
--- a/core/modules/user/user.module
+++ b/core/modules/user/user.module
@@ -2415,6 +2415,9 @@ function user_build_content($account, $view_mode = 'full', $langcode = NULL) {
   // Remove previously built content, if exists.
   $account->content = array();
 
+  // Allow modules to change the view mode.
+  drupal_alter('entity_view_mode', $view_mode, $account, $langcode);
+
   // Build fields content.
   field_attach_prepare_view('user', array($account->uid => $account), $view_mode, $langcode);
   entity_prepare_view('user', array($account->uid => $account), $langcode);