diff --git a/composer.json b/composer.json
index b6e5b90..cebe52b 100644
--- a/composer.json
+++ b/composer.json
@@ -13,7 +13,10 @@
         }
     ],
     "require": {
-    	"php": ">=7.1"
+    	"php": ">=7.1",
+        "roave/better-reflection": "dev-master",
+        "mindplay/composer-locator": "^2.1.3",
+        "symfony/event-dispatcher": "^2.3 || ^3 || ^4"
     },
     "require-dev": {
         "php-coveralls/php-coveralls": "^2.1",
diff --git a/src/BetterReflectionClassesExplorer.php b/src/BetterReflectionClassesExplorer.php
new file mode 100644
index 0000000..6d858f9
--- /dev/null
+++ b/src/BetterReflectionClassesExplorer.php
@@ -0,0 +1,237 @@
+<?php
+
+
+namespace TheCodingMachine\ClassExplorer;
+
+
+use phpDocumentor\Reflection\DocBlockFactoryInterface;
+use Roave\BetterReflection\BetterReflection;
+use Roave\BetterReflection\Identifier\IdentifierType;
+use Roave\BetterReflection\Reflection\ReflectionClass;
+use Roave\BetterReflection\Reflector\ClassReflector;
+use Roave\BetterReflection\SourceLocator\Type\AggregateSourceLocator;
+use Roave\BetterReflection\SourceLocator\Type\AutoloadSourceLocator;
+use Roave\BetterReflection\SourceLocator\Type\DirectoriesSourceLocator;
+use Roave\BetterReflection\SourceLocator\Type\EvaledCodeSourceLocator;
+use Roave\BetterReflection\SourceLocator\Type\FileIteratorSourceLocator;
+use Roave\BetterReflection\SourceLocator\Type\MemoizingSourceLocator;
+use Roave\BetterReflection\SourceLocator\Type\PhpInternalSourceLocator;
+use Symfony\Component\EventDispatcher\EventDispatcher;
+use TheCodingMachine\ClassExplorer\Events\IdentifierNotFoundEvent;
+use TheCodingMachine\ClassExplorer\Exceptions\ClassExplorerException;
+
+class BetterReflectionClassesExplorer
+{
+    /*
+     * Datastructure used as cache:
+     *
+     * [
+     *   "files" => [
+     *     "full/file/name.php" => [
+     *       "mtime" => 25346554
+     *       "classes" => [] // Classes, interfaces or traits, key is class name, value is irrelevent
+     *     ]
+     *   ],
+     *   "classes": [
+     *     "FQCN": [
+     *       "type": "interface|class|trait",
+     *       "internal" : true // Present if class is a system class like \Exception
+     *       "implements": [] // Direct level (does not contain the interfaces extended by the interface implemented)
+     *       "extends": [""] // The parents hierarchy
+     *       "uses": [] // Only the traits for this class, not the parent classes.
+     *       "dependencies": [] // classes, interfaces, traits implementing/extending/using this object => key is class/interface/trait name
+     *       "path" => "" // Relative path to the file (or absolute path if not part of project)
+     *     ]
+     *   ]
+     * ]
+     */
+    private $data;
+
+    /**
+     * @var EventDispatcher
+     */
+    private $eventDispatcher;
+
+    public function __construct(EventDispatcher $eventDispatcher, $data = ['files'=>[], 'classes'=>[]])
+    {
+        $this->eventDispatcher = $eventDispatcher;
+        $this->data = $data;
+    }
+
+    public function getClasses()
+    {
+        $rootPath = \ComposerLocator::getRootPath().'/';
+        $data = $this->data;
+        $phpFiles = \iterator_to_array(PackageSourceLocator::getVendorPhpFiles());
+
+        // From the list of deleted files, let's remove the list of interfaces/classes/... that were in those files.
+        // Also, let's flag for reloading the classes that need to be reloaded.
+        $deletedFiles = $this->getDeletedFiles($phpFiles);
+
+        $deletedClasses = [];
+        foreach ($deletedFiles as $path => $definition) {
+            $deletedClasses += $definition['classes'];
+        }
+
+        $toRefreshClasses = [];
+        foreach ($deletedClasses as $deletedClass => $foo) {
+            $toRefreshClasses += $data['classes'][$deletedClass]['dependencies'];
+        }
+
+        // A class cannot be "to refresh" if it is deleted also.
+        $toRefreshClasses = \array_diff_key($toRefreshClasses, $deletedClasses);
+
+        $modifiedPhpFiles = $this->getModifiedFiles($phpFiles);
+
+        // Let's reset the files datastructure for modified files:
+        foreach ($modifiedPhpFiles as $path => $def) {
+            $data['files'][$path]['classes'] = [];
+            $data['files'][$path]['mtime'] = \filemtime($path);
+        }
+
+        $betterReflection = new BetterReflection();
+        $astLocator = $betterReflection->astLocator();
+
+        // TODO: FileIteratorSourceLocator does not benefit from the MemoizingSourceLocator declared in $betterReflection->classReflector.
+        $filesSourceLocator = new FileIteratorSourceLocator(new \ArrayIterator($modifiedPhpFiles), $astLocator);
+        $reflector = $betterReflection->classReflector();
+        /** @var ReflectionClass[] $classes */
+        $classes = $filesSourceLocator->locateIdentifiersByType(
+            $reflector,
+            new IdentifierType(IdentifierType::IDENTIFIER_CLASS)
+        );
+
+        foreach ($toRefreshClasses as $toRefreshClass) {
+            $classes[] = $reflector->reflect($toRefreshClass);
+        }
+
+        foreach ($classes as $class) {
+            if (!isset($data['files'][$class->getFileName()])) {
+                throw new ClassExplorerException('Unexpected missing key: class '.$class->getName().' is supposed to be part of file "'.$class->getFileName().'" but this file was not found in list of modified files"');
+            }
+            try {
+
+                $data['files'][$class->getFileName()]['classes'][$class->getName()] = true;
+                if ($class->isInterface()) {
+                    $type = 'interface';
+                } elseif ($class->isTrait()) {
+                    $type = 'trait';
+                } else {
+                    $type = 'class';
+                }
+                $def = [
+                    'type' => $type
+                ];
+                $extends = [];
+                $parentClass = $class;
+                while ($parentClass = $parentClass->getParentClass()) {
+                    $extends[] = $parentClass->getName();
+                }
+                $def['extends'] = $extends;
+                $def['implements'] = $class->getInterfaceNames();
+                $def['uses'] = array_map(function($trait) { return $trait->getName(); }, $class->getTraits());
+                $def['path'] = $this->getRelativePathIfAvailable($class->getFileName(), $rootPath);
+            } catch (\Roave\BetterReflection\Reflector\Exception\IdentifierNotFound $e) {
+                $this->eventDispatcher->dispatch(IdentifierNotFoundEvent::NAME, new IdentifierNotFoundEvent($e->getIdentifier()->getName()));
+                continue;
+            }
+
+            $data['classes'][$class->getName()] = $def;
+        }
+
+        $data['classes'] = $this->generateDependenciesData($data['classes']);
+
+        $this->data = $data;
+
+        return $data;
+    }
+
+    /**
+     * Returns the list of files that have disappeared.
+     *
+     * @param \SplFileInfo[] $files Typically the result of a call to PackageSourceLocator::getVendorPhpFiles casted to array
+     * @return array[] Key: full path, Value: Same structure as $this->data['files'][]
+     */
+    private function getDeletedFiles(array $files): array
+    {
+        return \array_diff_key($this->data['files'], $files);
+    }
+
+    /**
+     * Returns modified files OR new files.
+     *
+     * @param \SplFileInfo[] $files
+     * @return \SplFileInfo[]
+     */
+    private function getModifiedFiles(array $files): array
+    {
+        $oldFiles = $this->data['files'];
+        return \array_filter($files, function(\SplFileInfo $file, $path) use ($oldFiles) {
+            return !isset($oldFiles[$path]) || (isset($oldFiles[$path]) && $oldFiles[$path]['mtime'] !== $file->getMTime());
+        }, ARRAY_FILTER_USE_BOTH);
+    }
+
+    /**
+     * Returns the relative path to $rootPath or if $path is not part of $rootPath, the absolute path.
+     *
+     * @param string $path
+     * @param string $rootPath supposed to end with '/'
+     * @return string
+     */
+    private function getRelativePathIfAvailable(string $path, string $rootPath): string
+    {
+        if (strpos($path, $rootPath) === 0) {
+            return substr($path, \strlen($rootPath));
+        }
+        return $path;
+    }
+
+    /**
+     * @param array[] $classes The array of $data['classes']
+     * @return array[]
+     */
+    private function generateDependenciesData(array $classes): array
+    {
+        foreach ($classes as &$class) {
+            $class['dependencies'] = [];
+        }
+
+        foreach ($classes as $className => $class) {
+            if (isset($class['internal'])) {
+                continue;
+            }
+            foreach ($class['extends'] as $parent) {
+                // If we extend from a root class (like \Exception)
+                if (!isset($classes[$parent])) {
+                    $classes[$parent] = [
+                        'internal' => true,
+                    ];
+                }
+                $classes[$parent]['dependencies'][] = $className;
+            }
+
+            foreach ($class['implements'] as $interface) {
+                // If we extend from a root class (like \Exception)
+                if (!isset($classes[$interface])) {
+                    $classes[$interface] = [
+                        'internal' => true,
+                    ];
+                }
+                $classes[$interface]['dependencies'][] = $className;
+            }
+
+            foreach ($class['uses'] as $trait) {
+                // If we extend from a root class (like \Exception)
+                if (!isset($classes[$trait])) {
+                    $classes[$trait] = [
+                        'internal' => true,
+                    ];
+                }
+                $classes[$trait]['dependencies'][] = $className;
+            }
+
+        }
+
+        return $classes;
+    }
+}
diff --git a/src/Events/IdentifierNotFoundEvent.php b/src/Events/IdentifierNotFoundEvent.php
new file mode 100644
index 0000000..8fe5789
--- /dev/null
+++ b/src/Events/IdentifierNotFoundEvent.php
@@ -0,0 +1,31 @@
+<?php
+
+
+namespace TheCodingMachine\ClassExplorer\Events;
+
+
+use Symfony\Component\EventDispatcher\Event;
+
+class IdentifierNotFoundEvent extends Event
+{
+    const NAME = 'classes.explorers.identifier_not_found';
+
+    /**
+     * @var string
+     */
+    private $identifier;
+
+    public function __construct(string $identifier)
+    {
+
+        $this->identifier = $identifier;
+    }
+
+    /**
+     * @return string
+     */
+    public function getIdentifier(): string
+    {
+        return $this->identifier;
+    }
+}
\ No newline at end of file
diff --git a/src/Exceptions/ClassExplorerException.php b/src/Exceptions/ClassExplorerException.php
new file mode 100644
index 0000000..4bddbd5
--- /dev/null
+++ b/src/Exceptions/ClassExplorerException.php
@@ -0,0 +1,10 @@
+<?php
+
+
+namespace TheCodingMachine\ClassExplorer\Exceptions;
+
+
+class ClassExplorerException extends \Exception
+{
+
+}
\ No newline at end of file
diff --git a/src/Exceptions/PackageDetectionException.php b/src/Exceptions/PackageDetectionException.php
new file mode 100644
index 0000000..569c356
--- /dev/null
+++ b/src/Exceptions/PackageDetectionException.php
@@ -0,0 +1,18 @@
+<?php
+
+
+namespace TheCodingMachine\ClassExplorer\Exceptions;
+
+
+class PackageDetectionException extends ClassExplorerException
+{
+    public static function cannotLoadComposerLock(string $path): self
+    {
+        return new self("Unable to load composer.lock file in '$path')");
+    }
+
+    public static function unableToDecodeJson(): self
+    {
+        return new self("Unable to decode JSON in composer.lock");
+    }
+}
\ No newline at end of file
diff --git a/src/PackageSourceLocator.php b/src/PackageSourceLocator.php
new file mode 100644
index 0000000..c789b3e
--- /dev/null
+++ b/src/PackageSourceLocator.php
@@ -0,0 +1,137 @@
+<?php
+
+
+namespace TheCodingMachine\ClassExplorer;
+
+use RecursiveDirectoryIterator;
+use RecursiveIteratorIterator;
+use RegexIterator;
+use TheCodingMachine\ClassExplorer\Exceptions\PackageDetectionException;
+
+class PackageSourceLocator
+{
+    /**
+     * @return string[][] An array with 2 keys: "directories" and "files". Each value is an array of string
+     * @throws PackageDetectionException
+     */
+    public static function getVendorSources(): array
+    {
+        $rootPath = \ComposerLocator::getRootPath();
+
+        $packageLockContent = \file_get_contents($rootPath.'/composer.lock');
+        if ($packageLockContent === false) {
+            throw PackageDetectionException::cannotLoadComposerLock($rootPath.'/composer.lock');
+        }
+
+        $packageLock = json_decode($packageLockContent, true);
+        if ($packageLock === false) {
+            throw PackageDetectionException::unableToDecodeJson();
+        }
+
+        $directories = [];
+        $files = [];
+
+        foreach ($packageLock['packages'] as $packageDef) {
+            self::addDirectoriesAndFiles($packageDef, $directories, $files, false);
+        }
+        if ($packageLock['packages-dev']) {
+            foreach ($packageLock['packages-dev'] as $packageDef) {
+                // We are not sure that dev packages are installed so we allow failure to retrieve them.
+                self::addDirectoriesAndFiles($packageDef, $directories, $files, true);
+            }
+        }
+
+        // TODO: add support for exclude-from-classmap: https://getcomposer.org/doc/04-schema.md#exclude-files-from-classmaps
+
+        return ['directories' => $directories, 'files' => $files];
+    }
+
+    private static function addDirectoriesAndFiles(array $packageDef, array &$directories, array &$files, bool $canFail): void
+    {
+        if (!isset($packageDef['autoload'])) {
+            return;
+        }
+
+        $autoload = $packageDef['autoload'];
+        try {
+            $packagePath = \ComposerLocator::getPath($packageDef['name']).'/';
+        } catch (\RuntimeException $runtimeException) {
+            if ($canFail === true) {
+                return;
+            } else {
+                throw $runtimeException;
+            }
+        }
+
+        foreach (['psr-0', 'psr-4'] as $psrNumber) {
+            if (isset($autoload[$psrNumber])) {
+                foreach ($autoload[$psrNumber] as $dir) {
+                    if (\is_array($dir)) {
+                        foreach ($dir as $item) {
+                            $directories[] = $packagePath.$item;
+                        }
+                    } else {
+                        $directories[] = $packagePath.$dir;
+                    }
+                }
+            }
+        }
+        if (isset($autoload['classmap'])) {
+            foreach ($autoload['classmap'] as $file) {
+                if (\is_dir($packagePath.$file)) {
+                    $directories[] = $packagePath.$file;
+                } else {
+                    $files[] = $packagePath.$file;
+                }
+            }
+        }
+        if (isset($autoload['files'])) {
+            foreach ($autoload['files'] as $file) {
+                $files[] = $packagePath.$file;
+            }
+        }
+    }
+
+    /**
+     * Returns a list of all vendor PHP files.
+     * The key of the iterator is the absolute path of the file. The value is the SplFileInfo.
+     *
+     * @return \Iterator|\SplFileInfo[]
+     */
+    public static function getVendorPhpFiles(): \Iterator
+    {
+        $appendIterator = new \AppendIterator();
+        ['directories' => $directories, 'files' => $files] = self::getVendorSources();
+
+        foreach ($directories as $directory) {
+            $appendIterator->append(self::getPhpFilesForDir($directory));
+        }
+
+        $filesInfo = [];
+        foreach ($files as $file) {
+            $filesInfo[(string) $file] = new \SplFileInfo($file);
+        }
+
+        $appendIterator->append(new \ArrayIterator($filesInfo));
+        //$appendIterator->append(new \ArrayIterator(\array_flip($files)));
+
+        return $appendIterator;
+    }
+
+    /**
+     * @param string $directory
+     * @return \Iterator|\SplFileInfo[]
+     */
+    private static function getPhpFilesForDir(string $directory): \Iterator
+    {
+        // If there is an error in the directory (might happen with dependencies), let's ignore that.
+        if (!\is_dir($directory)) {
+            return new \EmptyIterator();
+        }
+        $allFiles  = new RecursiveIteratorIterator(new RecursiveDirectoryIterator($directory, RecursiveDirectoryIterator::SKIP_DOTS));
+        // TODO: it would be better to keep the values as a SplFileInfo since we have to:
+        // check modification time
+        // use SplFileInfo in iterator from better-reflection
+        return new RegexIterator($allFiles, '/\.php$/i'/*, \RecursiveRegexIterator::GET_MATCH*/);
+    }
+}
diff --git a/tests/ClassesExplorerTest.php b/tests/ClassesExplorerTest.php
new file mode 100644
index 0000000..b25bb97
--- /dev/null
+++ b/tests/ClassesExplorerTest.php
@@ -0,0 +1,36 @@
+<?php
+
+namespace TheCodingMachine\ClassExplorer;
+
+
+use PHPUnit\Framework\TestCase;
+use Symfony\Component\EventDispatcher\EventDispatcher;
+use TheCodingMachine\ClassExplorer\Events\IdentifierNotFoundEvent;
+
+class ClassesExplorerTest extends TestCase
+{
+
+    public function testGetClasses()
+    {
+        $eventDispatcher = new EventDispatcher();
+        $classExplorer = new BetterReflectionClassesExplorer($eventDispatcher);
+
+        $notFounds = [];
+
+        $eventDispatcher->addListener(IdentifierNotFoundEvent::NAME, function(IdentifierNotFoundEvent $event) use (&$notFounds) {
+            $notFounds[] = $event->getIdentifier();
+        });
+
+        $classes = $classExplorer->getClasses();
+        var_export($classes);
+
+        $this->assertContains('Composer\\Plugin\\PluginInterface', $notFounds);
+
+        $this->assertSame('class', $classes['classes']['Roave\\BetterReflection\\BetterReflection']['type']);
+        $this->assertSame('vendor/roave/better-reflection/src/BetterReflection.php', $classes['classes']['Roave\\BetterReflection\\BetterReflection']['path']);
+
+        $classes2 = $classExplorer->getClasses();
+
+        $this->assertEquals($classes, $classes2);
+    }
+}
diff --git a/tests/PackageSourceLocatorTest.php b/tests/PackageSourceLocatorTest.php
new file mode 100644
index 0000000..1adbdc7
--- /dev/null
+++ b/tests/PackageSourceLocatorTest.php
@@ -0,0 +1,35 @@
+<?php
+
+namespace TheCodingMachine\ClassExplorer;
+
+
+use PHPUnit\Framework\TestCase;
+
+class PackageSourceLocatorTest extends TestCase
+{
+
+    public function testGetVendorSources(): void
+    {
+        $sources = PackageSourceLocator::getVendorSources();
+
+        ['directories' => $directories, 'files' => $files] = $sources;
+
+        $this->assertContains(\dirname(__DIR__).'/vendor/roave/better-reflection/src', $directories);
+        $this->assertContains(\dirname(__DIR__).'/vendor/mindplay/composer-locator/src/ComposerLocator.php', $files);
+    }
+
+    public function testGetVendorPhpFiles(): void
+    {
+        $phpFiles = PackageSourceLocator::getVendorPhpFiles();
+
+        $phpFiles = iterator_to_array($phpFiles);
+        $files = [];
+
+        foreach ($phpFiles as $fileInfo) {
+            $files[(string) $fileInfo] = true;
+        }
+
+        $this->assertArrayHasKey(\dirname(__DIR__).'/vendor/mindplay/composer-locator/src/ComposerLocator.php', $files);
+        $this->assertArrayHasKey(\dirname(__DIR__).'/vendor/roave/better-reflection/src/SourceLocator/Type/SourceLocator.php', $files);
+    }
+}