diff -u b/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
--- b/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -954,16 +954,11 @@
  * by this function. Settings should be used over configuration for read-only,
  * possibly low bootstrap configuration that is environment specific.
  *
- * @param string $name
- *   The name of the setting to return.
- * @param mixed $default
- *   (optional) The default value to use if this setting is not set.
- *
- * @return mixed
- *   The value of the setting, the provided default if not set.
+ * @return \Drupal\Component\Utility\Settings
+ *   The settings object.
  */
-function settings_get($name, $default = NULL) {
-  return Settings::$singleton->get($name, $default);
+function settings() {
+  return Settings::$singleton;
 }
 
 /**
@@ -1413,7 +1408,7 @@
   // response to reply to a subsequent request for a given URL without
   // revalidation. If a Vary header has been set in hook_boot(), it is assumed
   // that the module knows how to cache the page.
-  if (!isset($hook_boot_headers['vary']) && !settings_get('omit_vary_cookie')) {
+  if (!isset($hook_boot_headers['vary']) && !settings()->get('omit_vary_cookie')) {
     header('Vary: Cookie');
   }
 
@@ -2142,7 +2137,7 @@
           break;
 
         case DRUPAL_BOOTSTRAP_SESSION:
-          require_once DRUPAL_ROOT . '/' . settings_get('session_inc', 'core/includes/session.inc');
+          require_once DRUPAL_ROOT . '/' . settings()->get('session_inc', 'core/includes/session.inc');
           drupal_session_initialize();
           break;
 
@@ -2333,7 +2328,7 @@
     require_once DRUPAL_ROOT . '/' . $include;
   }
   // Check for a cache mode force from settings.php.
-  if (settings_get('page_cache_without_database')) {
+  if (settings()->get('page_cache_without_database')) {
     $cache_enabled = TRUE;
   }
   else {
@@ -3038,12 +3033,12 @@
   if (!isset($ip_address)) {
     $ip_address = $_SERVER['REMOTE_ADDR'];
 
-    if (settings_get('reverse_proxy', 0)) {
-      $reverse_proxy_header = settings_get('reverse_proxy_header', 'HTTP_X_FORWARDED_FOR');
+    if (settings()->get('reverse_proxy', 0)) {
+      $reverse_proxy_header = settings()->get('reverse_proxy_header', 'HTTP_X_FORWARDED_FOR');
       if (!empty($_SERVER[$reverse_proxy_header])) {
         // If an array of known reverse proxy IPs is provided, then trust
         // the XFF header if request really comes from one of them.
-        $reverse_proxy_addresses = settings_get('reverse_proxy_addresses', array());
+        $reverse_proxy_addresses = settings()->get('reverse_proxy_addresses', array());
 
         // Turn XFF header into an array.
         $forwarded = explode(',', $_SERVER[$reverse_proxy_header]);
@@ -3073,10 +3068,15 @@
  * classes, interfaces, and traits (PHP 5.4 and later). It's only dependency
  * is DRUPAL_ROOT. Otherwise it may be called as early as possible.
  *
+ * @param $class_loader
+ *   The name of class loader to use. This can be used to change the class
+ *   loader class when calling drupal_classloader() from settings.php. It is
+ *   ignored otherwise.
+ *
  * @return Symfony\Component\ClassLoader\UniversalClassLoader
  *   A UniversalClassLoader class instance (or extension thereof).
  */
-function drupal_classloader() {
+function drupal_classloader($class_loader = NULL) {
   // By default, use the UniversalClassLoader which is best for development,
   // as it does not break when code is moved on the file system. However, as it
   // is slow, allow to use the APC class loader in production.
@@ -3086,8 +3086,11 @@
 
     // Include the Symfony ClassLoader for loading PSR-0-compatible classes.
     require_once DRUPAL_ROOT . '/core/vendor/symfony/class-loader/Symfony/Component/ClassLoader/UniversalClassLoader.php';
+    if (!isset($class_loader) && class_exists('Drupal\Component\Utility\Settings', FALSE)) {
+      $class_loader = settings()->get('class_loader');
+    }
 
-    switch (settings_get('class_loader')) {
+    switch ($class_loader) {
       case 'apc':
         if (function_exists('apc_store')) {
           require_once DRUPAL_ROOT . '/core/vendor/symfony/class-loader/Symfony/Component/ClassLoader/ApcUniversalClassLoader.php';
diff -u b/core/includes/common.inc b/core/includes/common.inc
--- b/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -809,7 +809,7 @@
   $options['timeout'] = (float) $options['timeout'];
 
   // Use a proxy if one is defined and the host is not on the excluded list.
-  $proxy_server = settings_get('proxy_server', '');
+  $proxy_server = settings()->get('proxy_server', '');
   if ($proxy_server && _drupal_http_use_proxy($uri['host'])) {
     // Set the scheme so we open a socket to the proxy server.
     $uri['scheme'] = 'proxy';
@@ -819,13 +819,13 @@
     unset($uri['query']);
 
     // Add in username and password to Proxy-Authorization header if needed.
-    if ($proxy_username = settings_get('proxy_username', '')) {
-      $proxy_password = settings_get('proxy_password', '');
+    if ($proxy_username = settings()->get('proxy_username', '')) {
+      $proxy_password = settings()->get('proxy_password', '');
       $options['headers']['Proxy-Authorization'] = 'Basic ' . base64_encode($proxy_username . (!empty($proxy_password) ? ":" . $proxy_password : ''));
     }
     // Some proxies reject requests with any User-Agent headers, while others
     // require a specific one.
-    $proxy_user_agent = settings_get('proxy_user_agent', '');
+    $proxy_user_agent = settings()->get('proxy_user_agent', '');
     // The default value matches neither condition.
     if ($proxy_user_agent === NULL) {
       unset($options['headers']['User-Agent']);
@@ -838,7 +838,7 @@
   switch ($uri['scheme']) {
     case 'proxy':
       // Make the socket connection to a proxy server.
-      $socket = 'tcp://' . $proxy_server . ':' . settings_get('proxy_port', 8080);
+      $socket = 'tcp://' . $proxy_server . ':' . settings()->get('proxy_port', 8080);
       // The Host header still needs to match the real request.
       $options['headers']['Host'] = $uri['host'];
       $options['headers']['Host'] .= isset($uri['port']) && $uri['port'] != 80 ? ':' . $uri['port'] : '';
@@ -1068,7 +1068,7 @@
  *   TRUE if a proxy should be used for this host.
  */
 function _drupal_http_use_proxy($host) {
-  $proxy_exceptions = settings_get('proxy_exceptions', array('localhost', '127.0.0.1'));
+  $proxy_exceptions = settings()->get('proxy_exceptions', array('localhost', '127.0.0.1'));
   return !in_array(strtolower($host), $proxy_exceptions, TRUE);
 }
 
@@ -4757,10 +4757,10 @@
  * Loads code for subsystems and modules, and registers stream wrappers.
  */
 function _drupal_bootstrap_code() {
-  require_once DRUPAL_ROOT . '/' . settings_get('path_inc', 'core/includes/path.inc');
+  require_once DRUPAL_ROOT . '/' . settings()->get('path_inc', 'core/includes/path.inc');
   require_once DRUPAL_ROOT . '/core/includes/theme.inc';
   require_once DRUPAL_ROOT . '/core/includes/pager.inc';
-  require_once DRUPAL_ROOT . '/' . settings_get('menu_inc', 'core/includes/menu.inc');
+  require_once DRUPAL_ROOT . '/' . settings()->get('menu_inc', 'core/includes/menu.inc');
   require_once DRUPAL_ROOT . '/core/includes/tablesort.inc';
   require_once DRUPAL_ROOT . '/core/includes/file.inc';
   require_once DRUPAL_ROOT . '/core/includes/unicode.inc';
diff -u b/core/includes/database.inc b/core/includes/database.inc
--- b/core/includes/database.inc
+++ b/core/includes/database.inc
@@ -905,7 +905,7 @@
     // Five minutes is long enough to allow the slave to break and resume
     // interrupted replication without causing problems on the Drupal site from
     // the old data.
-    $duration = settings_get('maximum_replication_lag', 300);
+    $duration = settings()->get('maximum_replication_lag', 300);
     // Set session variable with amount of time to delay before using slave.
     $_SESSION['ignore_slave_server'] = REQUEST_TIME + $duration;
   }
diff -u b/core/includes/install.core.inc b/core/includes/install.core.inc
--- b/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -279,7 +279,7 @@
   require_once DRUPAL_ROOT . '/core/includes/file.inc';
   require_once DRUPAL_ROOT . '/core/includes/install.inc';
   require_once DRUPAL_ROOT . '/core/includes/schema.inc';
-  require_once DRUPAL_ROOT . '/' . settings_get('path_inc', 'core/includes/path.inc');
+  require_once DRUPAL_ROOT . '/' . settings()->get('path_inc', 'core/includes/path.inc');
 
   // Load module basics (needed for hook invokes).
   include_once DRUPAL_ROOT . '/core/includes/module.inc';
diff -u b/core/includes/theme.maintenance.inc b/core/includes/theme.maintenance.inc
--- b/core/includes/theme.maintenance.inc
+++ b/core/includes/theme.maintenance.inc
@@ -22,7 +22,7 @@
     return;
   }
 
-  require_once DRUPAL_ROOT . '/' . settings_get('path_inc', 'core/includes/path.inc');
+  require_once DRUPAL_ROOT . '/' . settings()->get('path_inc', 'core/includes/path.inc');
   require_once DRUPAL_ROOT . '/core/includes/theme.inc';
   require_once DRUPAL_ROOT . '/core/includes/common.inc';
   require_once DRUPAL_ROOT . '/core/includes/unicode.inc';
diff -u b/core/lib/Drupal/Component/Utility/Settings.php b/core/lib/Drupal/Component/Utility/Settings.php
--- b/core/lib/Drupal/Component/Utility/Settings.php
+++ b/core/lib/Drupal/Component/Utility/Settings.php
@@ -5,14 +5,60 @@
 class Settings {
+  /**
+   * @var array
+   */
   protected $storage;
+
+  /**
+   * @var Settings
+   */
   static $singleton;
+
+  /**
+   * @param array $settings
+   */
   function __construct(array $settings) {
     $this->storage = $settings;
     self::$singleton = $this;
   }
+
+  /**
+   * Trying to set a property is not allowed.
+   *
+   * @param $name
+   * @param $value
+   * @throws \Exception
+   */
   function __set($name, $value) {
     throw new \Exception('Nope.');
   }
-  function get($name, $default = NULL) {
+
+  /**
+   * Returns a setting.
+   *
+   * Settings can be set in settings.php in the $settings array and requested
+   * by this function. Settings should be used over configuration for read-only,
+   * possibly low bootstrap configuration that is environment specific.
+   *
+   * @param string $name
+   *   The name of the setting to return.
+   * @param mixed $default
+   *   (optional) The default value to use if this setting is not set.
+   *
+   * @return mixed
+   *   The value of the setting, the provided default if not set.
+   */
+  public function get($name, $default = NULL) {
     return isset($this->storage[$name]) ? $this->storage[$name] : $default;
   }
+
+  /**
+   * Returns all the settings. This is only used for testing purposes.
+   *
+   * @return array
+   *   All the settings.
+   */
+  public function getAll() {
+    return $this->storage;
+  }
+
 }
diff -u b/core/modules/system/lib/Drupal/system/Tests/Bootstrap/IpAddressTest.php b/core/modules/system/lib/Drupal/system/Tests/Bootstrap/IpAddressTest.php
--- b/core/modules/system/lib/Drupal/system/Tests/Bootstrap/IpAddressTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Bootstrap/IpAddressTest.php
@@ -58,14 +58,14 @@
     );
 
     // Proxy forwarding on but no proxy addresses defined.
-    $GLOBALS['settings']['reverse_proxy'] = 1;
+    $this->settingsSet('reverse_proxy',  1);
     $this->assertTrue(
       ip_address() == $this->remote_ip,
       'Proxy forwarding without trusted proxies got remote IP address.'
     );
 
     // Proxy forwarding on and proxy address not trusted.
-    $GLOBALS['settings']['reverse_proxy_addresses'] = array($this->proxy_ip, $this->proxy2_ip);
+    $this->settingsSet('reverse_proxy_addresses', array($this->proxy_ip, $this->proxy2_ip));
     drupal_static_reset('ip_address');
     $_SERVER['REMOTE_ADDR'] = $this->untrusted_ip;
     $this->assertTrue(
@@ -92,7 +92,7 @@
     );
 
     // Custom client-IP header.
-    $GLOBALS['settings']['reverse_proxy_header'] = 'HTTP_X_CLUSTER_CLIENT_IP';
+    $this->settingsSet('reverse_proxy_header', 'HTTP_X_CLUSTER_CLIENT_IP');
     $_SERVER['HTTP_X_CLUSTER_CLIENT_IP'] = $this->cluster_ip;
     drupal_static_reset('ip_address');
     $this->assertTrue(
diff -u b/core/modules/system/system.install b/core/modules/system/system.install
--- b/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -416,7 +416,7 @@
 
   // Verify the update.php access setting
   if ($phase == 'runtime') {
-    if (settings_get('update_free_access')) {
+    if (settings()->get('update_free_access')) {
       $requirements['update access'] = array(
         'value' => $t('Not protected'),
         'severity' => REQUIREMENT_ERROR,
diff -u b/core/update.php b/core/update.php
--- b/core/update.php
+++ b/core/update.php
@@ -209,7 +209,7 @@
     $output .= '</p>';
   }
 
-  if (settings_get('update_free_access')) {
+  if (settings()->get('update_free_access')) {
     $output .= "<p><strong>Reminder: don't forget to set the <code>\$settings['update_free_access']</code> value in your <code>settings.php</code> file back to <code>FALSE</code>.</strong></p>";
   }
 
@@ -327,7 +327,7 @@
   global $user;
 
   // Allow the global variable in settings.php to override the access check.
-  if (settings_get('update_free_access')) {
+  if (settings()->get('update_free_access')) {
     return TRUE;
   }
   // Calls to user_access() might fail during the Drupal 6 to 7 update process,
only in patch2:
unchanged:
--- a/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
@@ -8,6 +8,7 @@
 namespace Drupal\simpletest;
 
 use Drupal\Core\Database\Database;
+use Drupal\Component\Utility\Settings;
 use Drupal\Core\DependencyInjection\ContainerBuilder;
 use Drupal\Core\Database\ConnectionNotDefinedException;
 use Drupal\Core\DrupalKernel;
@@ -138,6 +139,11 @@
   protected $verboseDirectoryUrl;
 
   /**
+   * The settings array.
+   */
+  protected $originalSettings;
+
+  /**
    * Constructor for Test.
    *
    * @param $test_id
@@ -814,6 +820,7 @@ protected function prepareEnvironment() {
     }
 
     // Backup current in-memory configuration.
+    $this->originalSettings = settings()->getAll();
     $this->originalConf = $conf;
 
     // Backup statics and globals.
@@ -1012,6 +1019,7 @@ protected function tearDown() {
 
     // Restore original in-memory configuration.
     $conf = $this->originalConf;
+    new Settings($this->originalSettings);
 
     // Restore original statics and globals.
     drupal_container($this->originalContainer);
@@ -1092,6 +1100,22 @@ protected function exceptionHandler($exception) {
   }
 
   /**
+   * Changes in memory settings.
+   *
+   * @param $name
+   *   The name of the setting to return.
+   * @param $value
+   *   The value of the setting.
+   *
+   * @see \Drupal\Component\Utility\Settings::get()
+   */
+  protected function settingsSet($name, $value) {
+    $settings = settings()->getAll();
+    $settings[$name] = $value;
+    new Settings($settings);
+  }
+
+  /**
    * Generates a random string of ASCII characters of codes 32 to 126.
    *
    * The generated string includes alpha-numeric characters and common