diff --git a/core/modules/field/tests/modules/field_test/field_test.module b/core/modules/field/tests/modules/field_test/field_test.module
index 6dfbb15..935e849 100644
--- a/core/modules/field/tests/modules/field_test/field_test.module
+++ b/core/modules/field/tests/modules/field_test/field_test.module
@@ -285,3 +285,22 @@ function field_test_query_efq_table_prefixing_test_alter(&$query) {
   // exception if the EFQ does not properly prefix the base table.
   $query->join('test_entity','te2','%alias.ftid = test_entity.ftid');
 }
+
+/**
+ * Implements hook_field_formatter_settings_form_alter().
+ */
+function field_test_field_formatter_settings_form_alter(&$element, &$form_state, $context) {
+  $settings = $context['instance']['display'][$context['view_mode']]['settings'];
+  $element['field_test_formatter_settings_form_alter'] = array(
+    '#type' => 'textfield',
+    '#title' => t('Formatter settings form alter'),
+    '#default_value' => isset($settings['field_test_formatter_settings_form_alter']) ? $settings['field_test_formatter_settings_form_alter'] : '',
+  );
+}
+
+/**
+ * Implements hook_field_formatter_settings_summary_alter().
+ */
+function field_test_field_formatter_settings_summary_alter(&$summary, $context) {
+  $summary .= '<br />field_test_field_formatter_settings_summary_alter';
+}
diff --git a/core/modules/field_ui/field_ui.admin.inc b/core/modules/field_ui/field_ui.admin.inc
index 3034156..f719210 100644
--- a/core/modules/field_ui/field_ui.admin.inc
+++ b/core/modules/field_ui/field_ui.admin.inc
@@ -1059,6 +1059,17 @@ function field_ui_display_overview_form($form, &$form_state, $entity_type, $bund
         $settings_form = $function($field, $instance, $view_mode, $form, $form_state);
       }
 
+      // Allow other modules to alter the formatter settings form.
+      $context = array(
+        'module' => $formatter['module'],
+        'formatter' => $formatter,
+        'field' => $field,
+        'instance' => $instance,
+        'view_mode' => $view_mode,
+        'form' => $form,
+      );
+      drupal_alter('field_formatter_settings_form', $settings_form, $form_state, $context);
+
       if ($settings_form) {
         $table[$name]['format']['#cell_attributes'] = array('colspan' => 3);
         $table[$name]['format']['settings_edit_form'] = array(
@@ -1094,6 +1105,15 @@ function field_ui_display_overview_form($form, &$form_state, $entity_type, $bund
     else {
       // Display a summary of the current formatter settings.
       $summary = module_invoke($formatter['module'], 'field_formatter_settings_summary', $field, $instance, $view_mode);
+
+      // Allow other modules to alter the summary.
+      $context = array(
+        'field' => $field,
+        'instance' => $instance,
+        'view_mode' => $view_mode,
+      );
+      drupal_alter('field_formatter_settings_summary', $summary, $context);
+
       $table[$name]['settings_summary'] = array();
       $table[$name]['settings_edit'] = array();
       if ($summary) {
diff --git a/core/modules/field_ui/field_ui.api.php b/core/modules/field_ui/field_ui.api.php
index 80cbe78..db43fee 100644
--- a/core/modules/field_ui/field_ui.api.php
+++ b/core/modules/field_ui/field_ui.api.php
@@ -169,6 +169,56 @@ function hook_field_formatter_settings_form($field, $instance, $view_mode, $form
 }
 
 /**
+ * Alter the formatter settings form.
+ *
+ * @param $element
+ *   Form array as returned by hook_field_formatter_settings_form().
+ * @param $form_state
+ *   The form state of the (entire) configuration form.
+ * @param $context
+ *   An associative array with the following elements:
+ *   - 'module': The module that contains the definition of this formatter.
+ *   - 'formatter': The formatter type description array.
+ *   - 'field': The field structure being configured.
+ *   - 'instance': The instance structure being configured.
+ *   - 'view_mode': The view mode being configured.
+ *   - 'form': The (entire) configuration form array.
+ */
+function hook_field_formatter_settings_form_alter(&$element, &$form_state, $context) {
+  // Add a mysetting checkbox to the settings form for foo_field fields.
+  if ($context['field']['type'] == 'foo_field') {
+    $display = $context['instance']['display'][$context['view_mode']];
+    $element['mysetting'] = array(
+      '#type' => 'checkbox',
+      '#title' => t('My setting'),
+      '#default_value' => $display['settings']['mysetting'],
+    );
+  }
+}
+
+/**
+ * Alter the field formatter settings summary.
+ *
+ * @param $summary
+ *   The summary as returned by hook_field_formatter_settings_summary().
+ * @param $context
+ *   An associative array with the following elements:
+ *   - 'field': The field structure being configured.
+ *   - 'instance': The instance structure being configured.
+ *   - 'view_mode': The view mode being configured.
+ */
+function hook_field_formatter_settings_summary_alter(&$summary, $context) {
+  // Append a message to the summary when an instance of foo_field has
+  // mysetting set to TRUE for the current view mode.
+  if ($context['field']['type'] == 'foo_field') {
+    $display = $context['instance']['display'][$context['view_mode']];
+    if ($display['settings']['mysetting']) {
+      $summary .= '<br />' . t('My setting enabled.');
+    }
+  }
+}
+
+/**
  * Return a short summary for the current formatter settings of an instance.
  *
  * If an empty result is returned, the formatter is assumed to have no
diff --git a/core/modules/field_ui/lib/Drupal/field_ui/Tests/ManageDisplayTest.php b/core/modules/field_ui/lib/Drupal/field_ui/Tests/ManageDisplayTest.php
index 34ebf1c..2d45c6b 100644
--- a/core/modules/field_ui/lib/Drupal/field_ui/Tests/ManageDisplayTest.php
+++ b/core/modules/field_ui/lib/Drupal/field_ui/Tests/ManageDisplayTest.php
@@ -19,7 +19,7 @@ class ManageDisplayTest extends FieldUiTestBase {
    *
    * @var array
    */
-  public static $modules = array('search');
+  public static $modules = array('search', 'field_test');
 
   public static function getInfo() {
     return array(
@@ -75,6 +75,24 @@ class ManageDisplayTest extends FieldUiTestBase {
     $current_setting_value = $instance['display']['default']['settings'][$setting_name];
     $this->assertEqual($current_format, $format, t('The formatter was updated.'));
     $this->assertEqual($current_setting_value, $setting_value, t('The setting was updated.'));
+
+    // Assert that hook_field_formatter_settings_summary_alter() is called.
+    $this->assertText('field_test_field_formatter_settings_summary_alter');
+
+    // Click on the formatter settings button to open the formatter settings
+    // form.
+    $this->drupalPostAJAX(NULL, array(), "field_test_formatter_settings_edit");
+
+    // Assert that the field added in
+    // field_test_field_formatter_settings_form_alter() is present.
+    $fieldname = 'fields[field_test][settings_edit_form][settings][field_test_formatter_settings_form_alter]';
+    $this->assertField($fieldname, 'The field added in hook_field_formatter_settings_form_alter() is present on the settings form.');
+    $edit = array($fieldname => 'foo');
+    $this->drupalPostAJAX(NULL, $edit, "field_test_formatter_settings_update");
+
+    // Confirm that the settings are updated on the settings form.
+    $this->drupalPostAJAX(NULL, array(), "field_test_formatter_settings_edit");
+    $this->assertFieldByName($fieldname, 'foo');
   }
 
   /**