diff --git a/core/modules/comment/comment.module b/core/modules/comment/comment.module
index a6230f2..93de992 100644
--- a/core/modules/comment/comment.module
+++ b/core/modules/comment/comment.module
@@ -1023,6 +1023,14 @@ 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.
+  $context = array(
+    'entity_type' => 'comment',
+    'entity' => $comment,
+    'langcode' => $langcode,
+  );
+  drupal_alter('entity_view_mode', $view_mode, $context);
+
   // Build fields content.
   field_attach_prepare_view('comment', array($comment->cid => $comment), $view_mode, $langcode);
   entity_prepare_view('comment', array($comment->cid => $comment), $langcode);
diff --git a/core/modules/entity/entity.api.php b/core/modules/entity/entity.api.php
index 02d8754..48ba114 100644
--- a/core/modules/entity/entity.api.php
+++ b/core/modules/entity/entity.api.php
@@ -434,3 +434,15 @@ function hook_entity_prepare_view($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 array $context
+ *   An array with the keys entity_type, entity and langcode.
+ */
+function hook_entity_view_mode_alter(&$view_mode, array $context) {
+
+}
\ No newline at end of file
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 49d20a7..c3c7d68 100644
--- a/core/modules/node/node.module
+++ b/core/modules/node/node.module
@@ -1246,6 +1246,14 @@ 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.
+  $context = array(
+    'entity_type' => 'node',
+    'entity' => $node,
+    'langcode' => $langcode,
+  );
+  drupal_alter('entity_view_mode', $view_mode, $context);
+
   // The 'view' hook can be implemented to overwrite the default function
   // to display nodes.
   if (node_hook($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..6a5520e 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, array $context) {
+  // Only alter the view mode if we are on the test callback.
+  if ($view_mode = variable_get('node_test_change_view_mode', '')) {
+    $view_mode = $view_mode;
+  }
+}
diff --git a/core/modules/taxonomy/taxonomy.module b/core/modules/taxonomy/taxonomy.module
index 6697a0a..2d65e10 100644
--- a/core/modules/taxonomy/taxonomy.module
+++ b/core/modules/taxonomy/taxonomy.module
@@ -587,6 +587,14 @@ 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.
+  $context = array(
+    'entity_type' => 'taxonomy_term',
+    'entity' => $term,
+    'langcode' => $langcode,
+  );
+  drupal_alter('entity_view_mode', $view_mode, $context);
+
   field_attach_prepare_view('taxonomy_term', array($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 89706c4..552dde9 100644
--- a/core/modules/user/user.module
+++ b/core/modules/user/user.module
@@ -2405,6 +2405,14 @@ 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.
+  $context = array(
+    'entity_type' => 'user',
+    'entity' => $account,
+    'langcode' => $langcode,
+  );
+  drupal_alter('entity_view_mode', $view_mode, $context);
+
   // Build fields content.
   field_attach_prepare_view('user', array($account->uid => $account), $view_mode, $langcode);
   entity_prepare_view('user', array($account->uid => $account), $langcode);