diff --git a/core/includes/menu.inc b/core/includes/menu.inc
index d54fe06..1adc677 100644
--- a/core/includes/menu.inc
+++ b/core/includes/menu.inc
@@ -1805,7 +1805,7 @@ function menu_list_system_menus() {
  */
 function menu_main_menu() {
   $config = \Drupal::config('menu.settings');
-  $menu_enabled = module_exists('menu');
+  $menu_enabled = \Drupal::moduleHandler()->moduleExists('menu');
   // When menu module is not enabled, we need a hardcoded default value.
   $main_links_source = $menu_enabled ? $config->get('main_links') : 'main';
   return menu_navigation_links($main_links_source);
@@ -1816,7 +1816,7 @@ function menu_main_menu() {
  */
 function menu_secondary_menu() {
   $config = \Drupal::config('menu.settings');
-  $menu_enabled = module_exists('menu');
+  $menu_enabled = \Drupal::moduleHandler()->moduleExists('menu');
   // When menu module is not enabled, we need a hardcoded default value.
   $main_links_source = $menu_enabled ? $config->get('main_links') : 'main';
   $secondary_links_source = $menu_enabled ? $config->get('secondary_links') : 'account';
diff --git a/core/modules/block/custom_block/lib/Drupal/custom_block/CustomBlockTypeFormController.php b/core/modules/block/custom_block/lib/Drupal/custom_block/CustomBlockTypeFormController.php
index 15cd8f8..7273790 100644
--- a/core/modules/block/custom_block/lib/Drupal/custom_block/CustomBlockTypeFormController.php
+++ b/core/modules/block/custom_block/lib/Drupal/custom_block/CustomBlockTypeFormController.php
@@ -53,7 +53,7 @@ public function form(array $form, array &$form_state) {
       '#description' => t('Create a new revision by default for this block type.')
     );
 
-    if (module_exists('content_translation')) {
+    if ($this->moduleHandler->moduleExists('content_translation')) {
       $form['language'] = array(
         '#type' => 'details',
         '#title' => t('Language settings'),
diff --git a/core/modules/block/lib/Drupal/block/Tests/BlockTest.php b/core/modules/block/lib/Drupal/block/Tests/BlockTest.php
index af49957..8e045cf 100644
--- a/core/modules/block/lib/Drupal/block/Tests/BlockTest.php
+++ b/core/modules/block/lib/Drupal/block/Tests/BlockTest.php
@@ -251,7 +251,7 @@ function moveBlockToRegion(array $block, $region) {
    */
   function testBlockRehash() {
     \Drupal::moduleHandler()->install(array('block_test'));
-    $this->assertTrue(module_exists('block_test'), 'Test block module enabled.');
+    $this->assertTrue(\Drupal::moduleHandler()->moduleExists('block_test'), 'Test block module enabled.');
 
     // Clear the block cache to load the block_test module's block definitions.
     $this->container->get('plugin.manager.block')->clearCachedDefinitions();
diff --git a/core/modules/config/tests/config_test/lib/Drupal/config_test/ConfigTestFormController.php b/core/modules/config/tests/config_test/lib/Drupal/config_test/ConfigTestFormController.php
index 514311b..5390419 100644
--- a/core/modules/config/tests/config_test/lib/Drupal/config_test/ConfigTestFormController.php
+++ b/core/modules/config/tests/config_test/lib/Drupal/config_test/ConfigTestFormController.php
@@ -47,7 +47,7 @@ public function form(array $form, array &$form_state) {
       '#default_value' => $entity->get('style'),
       '#access' => FALSE,
     );
-    if (module_exists('image')) {
+    if ($this->moduleHandler->moduleExists('image')) {
       $form['style']['#access'] = TRUE;
       $form['style']['#options'] = image_style_options();
     }
diff --git a/core/modules/hal/lib/Drupal/hal/Normalizer/EntityNormalizer.php b/core/modules/hal/lib/Drupal/hal/Normalizer/EntityNormalizer.php
index a3aa448..0bedf76 100644
--- a/core/modules/hal/lib/Drupal/hal/Normalizer/EntityNormalizer.php
+++ b/core/modules/hal/lib/Drupal/hal/Normalizer/EntityNormalizer.php
@@ -92,7 +92,7 @@ public function denormalize($data, $class, $format = NULL, array $context = arra
     if (isset($data['langcode'])) {
       $langcode = $data['langcode'][0]['value'];
     }
-    elseif (module_exists('language')) {
+    elseif (\Drupal::moduleHandler()->moduleExists('language')) {
       $langcode = language_get_default_langcode($typed_data_ids['entity_type'], $typed_data_ids['bundle']);
     }
     else {
diff --git a/core/modules/history/lib/Drupal/history/Plugin/views/field/HistoryUserTimestamp.php b/core/modules/history/lib/Drupal/history/Plugin/views/field/HistoryUserTimestamp.php
index 8b0f502..fb0ea06 100644
--- a/core/modules/history/lib/Drupal/history/Plugin/views/field/HistoryUserTimestamp.php
+++ b/core/modules/history/lib/Drupal/history/Plugin/views/field/HistoryUserTimestamp.php
@@ -40,7 +40,7 @@ public function init(ViewExecutable $view, DisplayPluginBase $display, array &$o
     if (\Drupal::currentUser()->isAuthenticated()) {
       $this->additional_fields['created'] = array('table' => 'node_field_data', 'field' => 'created');
       $this->additional_fields['changed'] = array('table' => 'node_field_data', 'field' => 'changed');
-      if (module_exists('comment') && !empty($this->options['comments'])) {
+      if (\Drupal::moduleHandler()->moduleExists('comment') && !empty($this->options['comments'])) {
         $this->additional_fields['last_comment'] = array('table' => 'comment_entity_statistics', 'field' => 'last_comment_timestamp');
       }
     }
@@ -56,7 +56,7 @@ protected function defineOptions() {
 
   public function buildOptionsForm(&$form, &$form_state) {
     parent::buildOptionsForm($form, $form_state);
-    if (module_exists('comment')) {
+    if (\Drupal::moduleHandler()->moduleExists('comment')) {
       $form['comments'] = array(
         '#type' => 'checkbox',
         '#title' => t('Check for new comments as well'),
@@ -85,7 +85,7 @@ public function render(ResultRow $values) {
       $last_read = $this->getValue($values);
       $changed = $this->getValue($values, 'changed');
 
-      $last_comment = module_exists('comment') && !empty($this->options['comments']) ?  $this->getValue($values, 'last_comment') : 0;
+      $last_comment = \Drupal::moduleHandler()->moduleExists('comment') && !empty($this->options['comments']) ?  $this->getValue($values, 'last_comment') : 0;
 
       if (!$last_read && $changed > HISTORY_READ_LIMIT) {
         $mark = MARK_NEW;
diff --git a/core/modules/history/lib/Drupal/history/Plugin/views/filter/HistoryUserTimestamp.php b/core/modules/history/lib/Drupal/history/Plugin/views/filter/HistoryUserTimestamp.php
index 6b6b0db..ffd9a6f 100644
--- a/core/modules/history/lib/Drupal/history/Plugin/views/filter/HistoryUserTimestamp.php
+++ b/core/modules/history/lib/Drupal/history/Plugin/views/filter/HistoryUserTimestamp.php
@@ -80,7 +80,7 @@ public function query() {
 
     $clause = '';
     $clause2 = '';
-    if (module_exists('comment')) {
+    if (\Drupal::moduleHandler()->moduleExists('comment')) {
       $ces = $this->query->ensureTable('comment_entity_statistics', $this->relationship);
       $clause = ("OR $ces.last_comment_timestamp > (***CURRENT_TIME*** - $limit)");
       $clause2 = "OR $field < $ces.last_comment_timestamp";
diff --git a/core/modules/menu/menu.module b/core/modules/menu/menu.module
index 1ffddee..ee05ead 100644
--- a/core/modules/menu/menu.module
+++ b/core/modules/menu/menu.module
@@ -155,7 +155,7 @@ function menu_load($menu_name) {
 function menu_menu_insert(Menu $menu) {
   menu_cache_clear_all();
   // Invalidate the block cache to update menu-based derivatives.
-  if (module_exists('block')) {
+  if (\Drupal::moduleHandler()->moduleExists('block')) {
     \Drupal::service('plugin.manager.block')->clearCachedDefinitions();
   }
   // Make sure the menu is present in the active menus variable so that its
@@ -178,7 +178,7 @@ function menu_menu_insert(Menu $menu) {
 function menu_menu_update(Menu $menu) {
   menu_cache_clear_all();
   // Invalidate the block cache to update menu-based derivatives.
-  if (module_exists('block')) {
+  if (\Drupal::moduleHandler()->moduleExists('block')) {
     \Drupal::service('plugin.manager.block')->clearCachedDefinitions();
   }
 }
@@ -211,7 +211,7 @@ function menu_menu_delete(Menu $menu) {
   menu_cache_clear_all();
 
   // Invalidate the block cache to update menu-based derivatives.
-  if (module_exists('block')) {
+  if (\Drupal::moduleHandler()->moduleExists('block')) {
     \Drupal::service('plugin.manager.block')->clearCachedDefinitions();
   }
 }
diff --git a/core/modules/rest/lib/Drupal/rest/Plugin/rest/resource/DBLogResource.php b/core/modules/rest/lib/Drupal/rest/Plugin/rest/resource/DBLogResource.php
index 8b7cb99..bd05a5a 100644
--- a/core/modules/rest/lib/Drupal/rest/Plugin/rest/resource/DBLogResource.php
+++ b/core/modules/rest/lib/Drupal/rest/Plugin/rest/resource/DBLogResource.php
@@ -27,7 +27,7 @@ class DBLogResource extends ResourceBase {
    */
   public function routes() {
     // Only expose routes if the dblog module is enabled.
-    if (module_exists('dblog')) {
+    if (\Drupal::moduleHandler()->moduleExists('dblog')) {
       return parent::routes();
     }
     return new RouteCollection();
diff --git a/core/modules/simpletest/lib/Drupal/simpletest/Tests/DrupalUnitTestBaseTest.php b/core/modules/simpletest/lib/Drupal/simpletest/Tests/DrupalUnitTestBaseTest.php
index 715325a..953b38e 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/Tests/DrupalUnitTestBaseTest.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/Tests/DrupalUnitTestBaseTest.php
@@ -53,7 +53,7 @@ function testEnableModulesLoad() {
     $module = 'field_test';
 
     // Verify that the module does not exist yet.
-    $this->assertFalse(module_exists($module), "$module module not found.");
+    $this->assertFalse(\Drupal::moduleHandler()->moduleExists($module), "$module module not found.");
     $list = array_keys(\Drupal::moduleHandler()->getModuleList());
     $this->assertFalse(in_array($module, $list), "$module module not found in the extension handler's module list.");
     $list = \Drupal::moduleHandler()->getImplementations('permission');
@@ -63,7 +63,7 @@ function testEnableModulesLoad() {
     $this->enableModules(array($module));
 
     // Verify that the module exists.
-    $this->assertTrue(module_exists($module), "$module module found.");
+    $this->assertTrue(\Drupal::moduleHandler()->moduleExists($module), "$module module found.");
     $list = array_keys(\Drupal::moduleHandler()->getModuleList());
     $this->assertTrue(in_array($module, $list), "$module module found in the extension handler's module list.");
     $list = \Drupal::moduleHandler()->getImplementations('permission');
@@ -78,7 +78,7 @@ function testEnableModulesInstall() {
     $table = 'node';
 
     // Verify that the module does not exist yet.
-    $this->assertFalse(module_exists($module), "$module module not found.");
+    $this->assertFalse(\Drupal::moduleHandler()->moduleExists($module), "$module module not found.");
     $list = array_keys(\Drupal::moduleHandler()->getModuleList());
     $this->assertFalse(in_array($module, $list), "$module module not found in the extension handler's module list.");
     $list = \Drupal::moduleHandler()->getImplementations('permission');
@@ -92,7 +92,7 @@ function testEnableModulesInstall() {
     \Drupal::moduleHandler()->install(array($module));
 
     // Verify that the enabled module exists.
-    $this->assertTrue(module_exists($module), "$module module found.");
+    $this->assertTrue(\Drupal::moduleHandler()->moduleExists($module), "$module module found.");
     $list = array_keys(\Drupal::moduleHandler()->getModuleList());
     $this->assertTrue(in_array($module, $list), "$module module found in the extension handler's module list.");
     $list = \Drupal::moduleHandler()->getImplementations('permission');
diff --git a/core/modules/syslog/syslog.module b/core/modules/syslog/syslog.module
index 287cfaf..a93ee93 100644
--- a/core/modules/syslog/syslog.module
+++ b/core/modules/syslog/syslog.module
@@ -30,7 +30,7 @@ function syslog_help($path, $arg) {
  */
 function syslog_form_system_logging_settings_alter(&$form, &$form_state) {
   $config = \Drupal::config('syslog.settings');
-  $help = module_exists('help') ? ' ' . l(t('More information'), 'admin/help/syslog') . '.' : NULL;
+  $help = \Drupal::moduleHandler()->moduleExists('help') ? ' ' . l(t('More information'), 'admin/help/syslog') . '.' : NULL;
   $form['syslog_identity'] = array(
     '#type'          => 'textfield',
     '#title'         => t('Syslog identity'),
diff --git a/core/modules/system/lib/Drupal/system/Tests/Module/ModuleApiTest.php b/core/modules/system/lib/Drupal/system/Tests/Module/ModuleApiTest.php
index 0d184b6..68dae37 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Module/ModuleApiTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Module/ModuleApiTest.php
@@ -144,10 +144,10 @@ function testDependencyResolution() {
     // are not already enabled. (If they were, the tests below would not work
     // correctly.)
     \Drupal::moduleHandler()->install(array('module_test'), FALSE);
-    $this->assertTrue(module_exists('module_test'), 'Test module is enabled.');
-    $this->assertFalse(module_exists('forum'), 'Forum module is disabled.');
-    $this->assertFalse(module_exists('ban'), 'Ban module is disabled.');
-    $this->assertFalse(module_exists('xmlrpc'), 'XML-RPC module is disabled.');
+    $this->assertTrue(\Drupal::moduleHandler()->moduleExists('module_test'), 'Test module is enabled.');
+    $this->assertFalse(\Drupal::moduleHandler()->moduleExists('forum'), 'Forum module is disabled.');
+    $this->assertFalse(\Drupal::moduleHandler()->moduleExists('ban'), 'Ban module is disabled.');
+    $this->assertFalse(\Drupal::moduleHandler()->moduleExists('xmlrpc'), 'XML-RPC module is disabled.');
 
     // First, create a fake missing dependency. Forum depends on ban, which
     // depends on a made-up module, foo. Nothing should be installed.
@@ -155,7 +155,7 @@ function testDependencyResolution() {
     drupal_static_reset('system_rebuild_module_data');
     $result = \Drupal::moduleHandler()->install(array('forum'));
     $this->assertFalse($result, '\Drupal\Core\Extension\ModuleHandler::install() returns FALSE if dependencies are missing.');
-    $this->assertFalse(module_exists('forum'), '\Drupal\Core\Extension\ModuleHandler::install() aborts if dependencies are missing.');
+    $this->assertFalse(\Drupal::moduleHandler()->moduleExists('forum'), '\Drupal\Core\Extension\ModuleHandler::install() aborts if dependencies are missing.');
 
     // Now, fix the missing dependency. Forum module depends on ban, but ban
     // depends on the XML-RPC module.
@@ -165,9 +165,9 @@ function testDependencyResolution() {
     $result = \Drupal::moduleHandler()->install(array('forum'));
     $this->assertTrue($result, '\Drupal\Core\Extension\ModuleHandler::install() returns the correct value.');
     // Verify that the fake dependency chain was installed.
-    $this->assertTrue(module_exists('ban') && module_exists('xmlrpc'), 'Dependency chain was installed.');
+    $this->assertTrue(\Drupal::moduleHandler()->moduleExists('ban') && \Drupal::moduleHandler()->moduleExists('xmlrpc'), 'Dependency chain was installed.');
     // Verify that the original module was installed.
-    $this->assertTrue(module_exists('forum'), 'Module installation with unlisted dependencies succeeded.');
+    $this->assertTrue(\Drupal::moduleHandler()->moduleExists('forum'), 'Module installation with unlisted dependencies succeeded.');
     // Finally, verify that the modules were enabled in the correct order.
     $module_order = \Drupal::state()->get('module_test.install_order') ?: array();
     $this->assertEqual($module_order, array('xmlrpc', 'ban', 'forum'), 'Modules were enabled in the correct order.');
@@ -201,9 +201,9 @@ function testDependencyResolution() {
     $result = \Drupal::moduleHandler()->install(array('forum'));
     $this->assertTrue($result, '\Drupal\Core\Extension\ModuleHandler::install() returns the correct value.');
     // Verify that the fake dependency chain was installed.
-    $this->assertTrue(module_exists('ban') && module_exists('xmlrpc'), 'Dependency chain was installed.');
+    $this->assertTrue(\Drupal::moduleHandler()->moduleExists('ban') && \Drupal::moduleHandler()->moduleExists('xmlrpc'), 'Dependency chain was installed.');
     // Verify that the original module was installed.
-    $this->assertTrue(module_exists('forum'), 'Module installation with version dependencies succeeded.');
+    $this->assertTrue(\Drupal::moduleHandler()->moduleExists('forum'), 'Module installation with version dependencies succeeded.');
     // Finally, verify that the modules were enabled in the correct order.
     $enable_order = \Drupal::state()->get('module_test.install_order') ?: array();
     $xmlrpc_position = array_search('xmlrpc', $enable_order);
diff --git a/core/modules/system/lib/Drupal/system/Tests/System/InfoAlterTest.php b/core/modules/system/lib/Drupal/system/Tests/System/InfoAlterTest.php
index c739dd9..2dbbccf 100644
--- a/core/modules/system/lib/Drupal/system/Tests/System/InfoAlterTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/System/InfoAlterTest.php
@@ -32,7 +32,7 @@ function testSystemInfoAlter() {
     // Enable seven and the test module.
     theme_enable(array('seven'));
     \Drupal::moduleHandler()->install(array('module_test'), FALSE);
-    $this->assertTrue(module_exists('module_test'), 'Test module is enabled.');
+    $this->assertTrue(\Drupal::moduleHandler()->moduleExists('module_test'), 'Test module is enabled.');
 
     // Verify that the rebuilt and altered theme info is returned.
     $info = system_get_info('theme', 'seven');
diff --git a/core/modules/system/lib/Drupal/system/Tests/System/MainContentFallbackTest.php b/core/modules/system/lib/Drupal/system/Tests/System/MainContentFallbackTest.php
index 4d59aa7..69b1bd3 100644
--- a/core/modules/system/lib/Drupal/system/Tests/System/MainContentFallbackTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/System/MainContentFallbackTest.php
@@ -58,7 +58,7 @@ function testMainContentFallback() {
     $this->drupalPostForm(NULL, NULL, t('Uninstall'));
     $this->assertText(t('The selected modules have been uninstalled.'), 'Modules status has been updated.');
     $this->rebuildContainer();
-    $this->assertFalse(module_exists('block'), 'Block module uninstall.');
+    $this->assertFalse(\Drupal::moduleHandler()->moduleExists('block'), 'Block module uninstall.');
 
     // At this point, no region is filled and fallback should be triggered.
     $this->drupalGet('admin/config/system/site-information');
@@ -92,6 +92,6 @@ function testMainContentFallback() {
     $this->drupalPostForm('admin/modules', $edit, t('Save configuration'));
     $this->assertText(t('The configuration options have been saved.'), 'Modules status has been updated.');
     $this->rebuildContainer();
-    $this->assertTrue(module_exists('block'), 'Block module re-enabled.');
+    $this->assertTrue(\Drupal::moduleHandler()->moduleExists('block'), 'Block module re-enabled.');
   }
 }