diff --git a/CHANGELOG.md b/CHANGELOG.md
index 67fa8345b9..15fb561bca 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,10 @@ Version 4.0.0-dev
 * In formatting-preserving pretty printer:
   * Improved formatting of elements inserted into multi-line arrays.
 
+### Removed
+
+* The `Autoloader` class has been removed. It is not required to use the Composer autoloader.
+
 Version 4.0.0-alpha3 (2017-12-26)
 ---------------------------------
 
diff --git a/UPGRADE-4.0.md b/UPGRADE-4.0.md
index afa9685d52..ca36d5d864 100644
--- a/UPGRADE-4.0.md
+++ b/UPGRADE-4.0.md
@@ -73,4 +73,5 @@ Because HHVM does not support PHP 7, HHVM is no longer supported.
 * The XML serializer has been removed. As such, the classes `Serializer\XML`, and
   `Unserializer\XML`, as well as the interfaces `Serializer` and `Unserializer` no longer exist.
 * The `BuilderAbstract` class has been removed. It's functionality is moved into `BuilderHelpers`.
-  However, this is an internal class and should not be used directly.
\ No newline at end of file
+  However, this is an internal class and should not be used directly.
+* The `Autoloader` class has been removed in favor of relying on the Composer autoloader.
\ No newline at end of file
diff --git a/lib/PhpParser/Autoloader.php b/lib/PhpParser/Autoloader.php
deleted file mode 100644
index 50b3edbcec..0000000000
--- a/lib/PhpParser/Autoloader.php
+++ /dev/null
@@ -1,40 +0,0 @@
-<?php declare(strict_types=1);
-
-namespace PhpParser;
-
-/**
- * @codeCoverageIgnore
- */
-class Autoloader
-{
-    /** @var bool Whether the autoloader has been registered. */
-    private static $registered = false;
-
-    /**
-     * Registers PhpParser\Autoloader as an SPL autoloader.
-     *
-     * @param bool $prepend Whether to prepend the autoloader instead of appending
-     */
-    public static function register(bool $prepend = false) {
-        if (self::$registered === true) {
-            return;
-        }
-
-        spl_autoload_register([__CLASS__, 'autoload'], true, $prepend);
-        self::$registered = true;
-    }
-
-    /**
-     * Handles autoloading of classes.
-     *
-     * @param string $class A class name.
-     */
-    public static function autoload(string $class) {
-        if (0 === strpos($class, 'PhpParser\\')) {
-            $fileName = __DIR__ . strtr(substr($class, 9), '\\', '/') . '.php';
-            if (file_exists($fileName)) {
-                require $fileName;
-            }
-        }
-    }
-}
diff --git a/lib/bootstrap.php b/lib/bootstrap.php
deleted file mode 100644
index db39c37b64..0000000000
--- a/lib/bootstrap.php
+++ /dev/null
@@ -1,6 +0,0 @@
-<?php declare(strict_types=1);
-
-if (!class_exists(PhpParser\Autoloader::class)) {
-    require __DIR__ . '/PhpParser/Autoloader.php';
-}
-PhpParser\Autoloader::register();
diff --git a/test/PhpParser/AutoloaderTest.php b/test/PhpParser/AutoloaderTest.php
deleted file mode 100644
index c30e03e292..0000000000
--- a/test/PhpParser/AutoloaderTest.php
+++ /dev/null
@@ -1,18 +0,0 @@
-<?php declare(strict_types=1);
-
-namespace PhpParser;
-
-/* The autoloader is already active at this point, so we only check effects here. */
-
-use PHPUnit\Framework\TestCase;
-
-class AutoloaderTest extends TestCase
-{
-    public function testClassExists() {
-        $this->assertTrue(class_exists(NodeVisitorAbstract::class));
-        $this->assertFalse(class_exists('PHPParser_NodeVisitor_NameResolver'));
-
-        $this->assertFalse(class_exists('PhpParser\FooBar'));
-        $this->assertFalse(class_exists('PHPParser_FooBar'));
-    }
-}
diff --git a/test_old/run.php b/test_old/run.php
index 31846cf63f..2d7cdaccb6 100644
--- a/test_old/run.php
+++ b/test_old/run.php
@@ -110,8 +110,7 @@ function showHelp($error) {
         showHelp('Test type must be one of: PHP5, PHP7 or Symfony');
 }
 
-require_once __DIR__ . '/../lib/PhpParser/Autoloader.php';
-PhpParser\Autoloader::register();
+require_once __DIR__ . '/../vendor/autoload.php';
 
 $lexer = new PhpParser\Lexer\Emulative(['usedAttributes' => [
     'comments', 'startLine', 'endLine', 'startTokenPos', 'endTokenPos',