diff --git a/.travis.yml b/.travis.yml
index f02fefcb1..1140053c0 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -23,10 +23,15 @@ matrix:
     - php: 5.6
     - php: 7.0
     - php: 7.1
+      env: PHPSTAN=1
     - php: 7.2
+      env: PHPSTAN=1
     - php: 7.3
+      env: PHPSTAN=1
     - php: 7.3
-      env: deps=high
+      env:
+        - deps=high
+        - PHPSTAN=1
     - php: nightly
   fast_finish: true
   allow_failures:
@@ -58,6 +63,11 @@ before_script:
 script:
   # run test suite directories in parallel using GNU parallel
   - ls -d tests/Composer/Test/* | grep -v TestCase.php | parallel --gnu --keep-order 'echo "Running {} tests"; ./vendor/bin/phpunit -c tests/complete.phpunit.xml --colors=always {} || (echo -e "\e[41mFAILED\e[0m {}" && exit 1);'
+  # Run PHPStan
+  - if [[ $PHPSTAN == "1" ]]; then
+      composer require --dev phpstan/phpstan-shim:^0.11 --ignore-platform-reqs &&
+      vendor/bin/phpstan.phar analyse src tests --configuration=phpstan/config.neon --autoload-file=phpstan/autoload.php;
+    fi
 
 before_deploy:
   - php -d phar.readonly=0 bin/compile
diff --git a/phpstan/autoload.php b/phpstan/autoload.php
new file mode 100644
index 000000000..7d1ed7671
--- /dev/null
+++ b/phpstan/autoload.php
@@ -0,0 +1,5 @@
+<?php
+
+require_once __DIR__ . '/../vendor/autoload.php';
+
+require_once __DIR__ . '/../src/bootstrap.php';
diff --git a/phpstan/config.neon b/phpstan/config.neon
new file mode 100644
index 000000000..5f77d5cd1
--- /dev/null
+++ b/phpstan/config.neon
@@ -0,0 +1,38 @@
+parameters:
+    level: 0
+    excludes_analyse:
+        - 'tests/Composer/Test/Fixtures'
+        - 'tests/Composer/Test/Autoload/Fixtures'
+        - 'tests/Composer/Test/Plugin/Fixtures'
+    ignoreErrors:
+        # unused parameters
+        - '~^Constructor of class Composer\\Repository\\VcsRepository has an unused parameter \$dispatcher\.$~'
+        - '~^Constructor of class Composer\\Repository\\PearRepository has an unused parameter \$dispatcher\.$~'
+        - '~^Constructor of class Composer\\Util\\Http\\CurlDownloader has an unused parameter \$disableTls\.$~'
+        - '~^Constructor of class Composer\\Util\\Http\\CurlDownloader has an unused parameter \$options\.$~'
+        - '~^Constructor of class Composer\\Repository\\PearRepository has an unused parameter \$config\.$~'
+
+        # unused uses
+        - '~^Anonymous function has an unused use \$io\.$~'
+        - '~^Anonymous function has an unused use \$cache\.$~'
+        - '~^Anonymous function has an unused use \$path\.$~'
+        - '~^Anonymous function has an unused use \$fileName\.$~'
+
+        # ion cube is not installed
+        - '~^Function ioncube_loader_\w+ not found\.$~'
+        # rar is not installed
+        - '~^Call to static method open\(\) on an unknown class RarArchive\.$~'
+        # imagick is not installed
+        - '~^Instantiated class Imagick not found\.$~'
+
+        # variables from global scope
+        - '~^Undefined variable: \$vendorDir$~'
+        - '~^Undefined variable: \$baseDir$~'
+
+        # always checked whether the class exists
+        - '~^Instantiated class Symfony\\Component\\Console\\Terminal not found\.$~'
+        - '~^Class Symfony\\Component\\Console\\Input\\StreamableInputInterface not found\.$~'
+
+        # parent call in test mocks
+        - '~^Composer\\Test\\Mock\\HttpDownloaderMock::__construct\(\) does not call parent constructor from Composer\\Util\\HttpDownloader\.$~'
+        - '~^Composer\\Test\\Mock\\InstallationManagerMock::__construct\(\) does not call parent constructor from Composer\\Installer\\InstallationManager\.$~'
diff --git a/src/Composer/DependencyResolver/PoolBuilder.php b/src/Composer/DependencyResolver/PoolBuilder.php
index 8ab6e5244..9eb3dc0d0 100644
--- a/src/Composer/DependencyResolver/PoolBuilder.php
+++ b/src/Composer/DependencyResolver/PoolBuilder.php
@@ -48,7 +48,7 @@ class PoolBuilder
 
     public function buildPool(array $repositories, array $rootAliases, Request $request)
     {
-        $this->pool = new Pool($this->filterRequires);
+        $pool = new Pool($this->filterRequires);
         $this->rootAliases = $rootAliases;
 
         // TODO do we really want the request here? kind of want a root requirements thingy instead
@@ -133,13 +133,13 @@ class PoolBuilder
             }
         }
 
-        $this->pool->setPackages($this->packages, $this->priorities);
+        $pool->setPackages($this->packages, $this->priorities);
 
         unset($this->aliasMap);
         unset($this->loadedNames);
         unset($this->nameConstraints);
 
-        return $this->pool;
+        return $pool;
     }
 
     private function loadPackage(PackageInterface $package, $repoIndex)
diff --git a/src/Composer/Downloader/GzipDownloader.php b/src/Composer/Downloader/GzipDownloader.php
index 9748b91ac..91be4593d 100644
--- a/src/Composer/Downloader/GzipDownloader.php
+++ b/src/Composer/Downloader/GzipDownloader.php
@@ -28,6 +28,7 @@ use Composer\IO\IOInterface;
  */
 class GzipDownloader extends ArchiveDownloader
 {
+    /** @var ProcessExecutor */
     protected $process;
 
     public function __construct(IOInterface $io, Config $config, HttpDownloader $downloader, EventDispatcher $eventDispatcher = null, Cache $cache = null, ProcessExecutor $process = null)
diff --git a/src/Composer/Downloader/RarDownloader.php b/src/Composer/Downloader/RarDownloader.php
index 2ebc3bf18..d0fbadcc6 100644
--- a/src/Composer/Downloader/RarDownloader.php
+++ b/src/Composer/Downloader/RarDownloader.php
@@ -32,6 +32,7 @@ use RarArchive;
  */
 class RarDownloader extends ArchiveDownloader
 {
+    /** @var ProcessExecutor */
     protected $process;
 
     public function __construct(IOInterface $io, Config $config, HttpDownloader $downloader, EventDispatcher $eventDispatcher = null, Cache $cache = null, ProcessExecutor $process = null)
diff --git a/src/Composer/Downloader/XzDownloader.php b/src/Composer/Downloader/XzDownloader.php
index 19e51c321..371ceda1b 100644
--- a/src/Composer/Downloader/XzDownloader.php
+++ b/src/Composer/Downloader/XzDownloader.php
@@ -28,6 +28,7 @@ use Composer\IO\IOInterface;
  */
 class XzDownloader extends ArchiveDownloader
 {
+    /** @var ProcessExecutor */
     protected $process;
 
     public function __construct(IOInterface $io, Config $config, HttpDownloader $downloader, EventDispatcher $eventDispatcher = null, Cache $cache = null, ProcessExecutor $process = null)
diff --git a/src/Composer/Downloader/ZipDownloader.php b/src/Composer/Downloader/ZipDownloader.php
index efa9fc994..bd8d3b499 100644
--- a/src/Composer/Downloader/ZipDownloader.php
+++ b/src/Composer/Downloader/ZipDownloader.php
@@ -33,7 +33,9 @@ class ZipDownloader extends ArchiveDownloader
     private static $hasZipArchive;
     private static $isWindows;
 
+    /** @var ProcessExecutor */
     protected $process;
+    /** @var ZipArchive|null */
     private $zipArchiveObject;
 
     public function __construct(IOInterface $io, Config $config, HttpDownloader $downloader, EventDispatcher $eventDispatcher = null, Cache $cache = null, ProcessExecutor $process = null)
diff --git a/src/Composer/Package/Locker.php b/src/Composer/Package/Locker.php
index 405d43261..68540581c 100644
--- a/src/Composer/Package/Locker.php
+++ b/src/Composer/Package/Locker.php
@@ -31,13 +31,21 @@ use Seld\JsonLint\ParsingException;
  */
 class Locker
 {
+    /** @var JsonFile */
     private $lockFile;
+    /** @var RepositoryManager */
     private $repositoryManager;
+    /** @var InstallationManager */
     private $installationManager;
+    /** @var string */
     private $hash;
+    /** @var string */
     private $contentHash;
+    /** @var ArrayLoader */
     private $loader;
+    /** @var ArrayDumper */
     private $dumper;
+    /** @var ProcessExecutor */
     private $process;
     private $lockDataCache;
 
diff --git a/src/Composer/Package/Version/VersionGuesser.php b/src/Composer/Package/Version/VersionGuesser.php
index 1c2fdf986..d655bc080 100644
--- a/src/Composer/Package/Version/VersionGuesser.php
+++ b/src/Composer/Package/Version/VersionGuesser.php
@@ -17,6 +17,7 @@ use Composer\Repository\Vcs\HgDriver;
 use Composer\IO\NullIO;
 use Composer\Semver\VersionParser as SemverVersionParser;
 use Composer\Util\Git as GitUtil;
+use Composer\Util\HttpDownloader;
 use Composer\Util\ProcessExecutor;
 use Composer\Util\Svn as SvnUtil;
 
diff --git a/src/Composer/Util/Bitbucket.php b/src/Composer/Util/Bitbucket.php
index d9f569b1b..ea02dfa0b 100644
--- a/src/Composer/Util/Bitbucket.php
+++ b/src/Composer/Util/Bitbucket.php
@@ -22,11 +22,17 @@ use Composer\Downloader\TransportException;
  */
 class Bitbucket
 {
+    /** @var IOInterface */
     private $io;
+    /** @var Config */
     private $config;
+    /** @var ProcessExecutor */
     private $process;
+    /** @var HttpDownloader */
     private $httpDownloader;
+    /** @var array */
     private $token = array();
+    /** @var int|null */
     private $time;
 
     const OAUTH2_ACCESS_TOKEN_URL = 'https://bitbucket.org/site/oauth2/access_token';
diff --git a/src/Composer/Util/Filesystem.php b/src/Composer/Util/Filesystem.php
index 1903f1c8d..805eda14b 100644
--- a/src/Composer/Util/Filesystem.php
+++ b/src/Composer/Util/Filesystem.php
@@ -23,6 +23,7 @@ use Symfony\Component\Finder\Finder;
  */
 class Filesystem
 {
+    /** @var ProcessExecutor */
     private $processExecutor;
 
     public function __construct(ProcessExecutor $executor = null)
@@ -537,6 +538,9 @@ class Filesystem
         return $size;
     }
 
+    /**
+     * @return ProcessExecutor
+     */
     protected function getProcess()
     {
         return $this->processExecutor;
diff --git a/src/Composer/Util/GitHub.php b/src/Composer/Util/GitHub.php
index c3046cb77..d6bfb62ca 100644
--- a/src/Composer/Util/GitHub.php
+++ b/src/Composer/Util/GitHub.php
@@ -22,9 +22,13 @@ use Composer\Downloader\TransportException;
  */
 class GitHub
 {
+    /** @var IOInterface */
     protected $io;
+    /** @var Config */
     protected $config;
+    /** @var ProcessExecutor */
     protected $process;
+    /** @var HttpDownloader */
     protected $httpDownloader;
 
     /**
diff --git a/src/Composer/Util/GitLab.php b/src/Composer/Util/GitLab.php
index 2a4867954..b2dbf2836 100644
--- a/src/Composer/Util/GitLab.php
+++ b/src/Composer/Util/GitLab.php
@@ -23,9 +23,13 @@ use Composer\Json\JsonFile;
  */
 class GitLab
 {
+    /** @var IOInterface */
     protected $io;
+    /** @var Config */
     protected $config;
+    /** @var ProcessExecutor */
     protected $process;
+    /** @var HttpDownloader */
     protected $httpDownloader;
 
     /**
diff --git a/src/Composer/Util/Loop.php b/src/Composer/Util/Loop.php
index 1be7d478b..c50cf4b02 100644
--- a/src/Composer/Util/Loop.php
+++ b/src/Composer/Util/Loop.php
@@ -20,7 +20,7 @@ use React\Promise\Promise;
  */
 class Loop
 {
-    private $io;
+    private $httpDownloader;
 
     public function __construct(HttpDownloader $httpDownloader)
     {
diff --git a/src/Composer/Util/StreamContextFactory.php b/src/Composer/Util/StreamContextFactory.php
index a87bc6d8b..f39c6dd38 100644
--- a/src/Composer/Util/StreamContextFactory.php
+++ b/src/Composer/Util/StreamContextFactory.php
@@ -14,6 +14,7 @@ namespace Composer\Util;
 
 use Composer\Composer;
 use Composer\CaBundle\CaBundle;
+use Composer\Downloader\TransportException;
 use Psr\Log\LoggerInterface;
 
 /**
diff --git a/tests/Composer/Test/Downloader/FileDownloaderTest.php b/tests/Composer/Test/Downloader/FileDownloaderTest.php
index 10ea401a8..89c538eab 100644
--- a/tests/Composer/Test/Downloader/FileDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/FileDownloaderTest.php
@@ -20,6 +20,8 @@ use Composer\Util\Loop;
 
 class FileDownloaderTest extends TestCase
 {
+    private $httpDownloader;
+
     protected function getDownloader($io = null, $config = null, $eventDispatcher = null, $cache = null, $httpDownloader = null, $filesystem = null)
     {
         $io = $io ?: $this->getMockBuilder('Composer\IO\IOInterface')->getMock();
diff --git a/tests/Composer/Test/Downloader/ZipDownloaderTest.php b/tests/Composer/Test/Downloader/ZipDownloaderTest.php
index b754af607..e69149271 100644
--- a/tests/Composer/Test/Downloader/ZipDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/ZipDownloaderTest.php
@@ -25,7 +25,7 @@ class ZipDownloaderTest extends TestCase
      * @var string
      */
     private $testDir;
-    private $prophet;
+    private $httpDownloader;
     private $io;
     private $config;
     private $package;