diff --git a/composer.json b/composer.json
index 6414c966d..d3ec88c62 100644
--- a/composer.json
+++ b/composer.json
@@ -11,7 +11,8 @@
     ],
     "require": {
         "php": ">=5.4",
-        "ext-mongodb": "^1.0.0"
+        "ext-mongodb": "^1.0.0",
+        "ext-hash": "*"
     },
     "autoload": {
         "psr-4": { "MongoDB\\": "src/" },
diff --git a/src/GridFS/Bucket.php b/src/GridFS/Bucket.php
new file mode 100644
index 000000000..fab95163c
--- /dev/null
+++ b/src/GridFS/Bucket.php
@@ -0,0 +1,171 @@
+<?php
+
+namespace MongoDB\GridFS;
+
+use MongoDB\Collection;
+use MongoDB\Database;
+use MongoDB\BSON\ObjectId;
+use MongoDB\Driver\ReadPreference;
+use MongoDB\Driver\WriteConcern;
+use MongoDB\Exception\InvalidArgumentException;
+use MongoDB\Exception\InvalidArgumentTypeException;
+use MongoDB\Exception\RuntimeException;
+use MongoDB\Exception\UnexpectedValueException;
+
+/**
+ * Bucket abstracts the GridFS files and chunks collections.
+ *
+ * @api
+ */
+class Bucket
+{
+    private $manager;
+    private $databaseName;
+    private $options;
+
+    private $filesCollection;
+    private $chunksCollection;
+
+    private $ensuredIndexes = false;
+
+    /**
+     * Constructs a GridFS bucket.
+     *
+     * Supported options:
+     *
+     *  * bucketName (string): The bucket name, which will be used as a prefix
+     *    for the files and chunks collections. Defaults to "fs".
+     *
+     *  * chunkSizeBytes (integer): The chunk size in bytes. Defaults to
+     *    261120 (i.e. 255 KiB).
+     *
+     *  * readPreference (MongoDB\Driver\ReadPreference): Read preference.
+     *
+     *  * writeConcern (MongoDB\Driver\WriteConcern): Write concern.
+     *
+     * @param Manager  $manager      Manager instance from the driver
+     * @param string   $databaseName Database name
+     * @param array    $options      Bucket options
+     * @throws InvalidArgumentException
+     */
+    public function __construct(Manager $manager, $databaseName, array $options = [])
+    {
+        $options += [
+            'bucketName' => 'fs',
+            'chunkSizeBytes' => 261120,
+        ];
+
+        if (isset($options['bucketName']) && ! is_string($options['bucketName'])) {
+            throw new InvalidArgumentTypeException('"bucketName" option', $options['bucketName'], 'string');
+        }
+
+        if (isset($options['chunkSizeBytes']) && ! is_integer($options['chunkSizeBytes'])) {
+            throw new InvalidArgumentTypeException('"chunkSizeBytes" option', $options['chunkSizeBytes'], 'integer');
+        }
+
+        if (isset($options['readPreference']) && ! $options['readPreference'] instanceof ReadPreference) {
+            throw new InvalidArgumentTypeException('"readPreference" option', $options['readPreference'], 'MongoDB\Driver\ReadPreference');
+        }
+
+        if (isset($options['writeConcern']) && ! $options['writeConcern'] instanceof WriteConcern) {
+            throw new InvalidArgumentTypeException('"writeConcern" option', $options['writeConcern'], 'MongoDB\Driver\WriteConcern');
+        }
+
+        $this->manager = $manager;
+        $this->databaseName = (string) $databaseName;
+        $this->options = $options;
+
+        $this->filesCollection = new Collection(
+            $manager,
+            sprintf('%s.%s.files', $this->databaseName, $options['bucketName']),
+            isset($options['writeConcern']) ? $options['writeConcern'] : null,
+            isset($options['readPreference']) ? $options['readPreference'] : null,
+        );
+
+        $this->chunksCollection = new Collection(
+            $manager,
+            sprintf('%s.%s.chunks', $this->databaseName, $options['bucketName']),
+            isset($options['writeConcern']) ? $options['writeConcern'] : null,
+            isset($options['readPreference']) ? $options['readPreference'] : null,
+        );
+    }
+
+    /**
+     * Opens a Stream for reading the contents of a file specified by ID.
+     *
+     * @param ObjectId $id
+     * @return Stream
+     */
+    public function openDownloadStream(ObjectId $id)
+    {
+        
+    }
+
+    /**
+     * Return the chunkSizeBytes option for this Bucket.
+     *
+     * @return integer
+     */
+    public function getChunkSizeBytes()
+    {
+        return $this->options['chunkSizeBytes'];
+    }
+
+    /**
+     * Opens a Stream for writing the contents of a file.
+     *
+     * @param ObjectId $id
+     * @return Stream
+     */
+    public function openUploadStream($filename, array $options = [])
+    {
+        
+    }
+
+    private function ensureIndexes()
+    {
+        // Indexes should only be ensured once before the first write operation
+        if ($this->ensuredIndexes) {
+            return;
+        }
+
+        if ( ! $this->isFilesCollectionEmpty()) {
+            return;
+        }
+
+        $this->ensureFilesIndex();
+        $this->ensureChunksIndex();
+
+        $this->ensuredIndexes = true;
+    }
+
+    private function ensureChunksIndex()
+    {
+        foreach ($this->chunksCollection->listIndexes() as $index) {
+            if ($index->isUnique() && $index->getKey() === ['files_id' => 1, 'n' => 1]) {
+                return;
+            }
+        }
+
+        $this->chunksCollection->createIndex(['files_id' => 1, 'n' => 1], ['unique' => true]);
+    }
+
+    private function ensureFilesIndex()
+    {
+        foreach ($this->filesCollection->listIndexes() as $index) {
+            if ($index->getKey() === ['filename' => 1, 'uploadDate' => 1]) {
+                return;
+            }
+        }
+
+        $this->filesCollection->createIndex(['filename' => 1, 'uploadDate' => 1]);
+    }
+
+    private function isFilesCollectionEmpty()
+    {
+        return null === $this->filesCollection->findOne([], [
+            'readPreference' => new ReadPreference(ReadPreference::RP_PRIMARY),
+            'projection' => ['_id' => 1],
+        ]);
+    }
+}
diff --git a/src/GridFS/StreamWrapper.php b/src/GridFS/StreamWrapper.php
new file mode 100644
index 000000000..6fe5cfd32
--- /dev/null
+++ b/src/GridFS/StreamWrapper.php
@@ -0,0 +1,180 @@
+<?php
+
+namespace MongoDB\GridFS;
+
+use MongoDB\Driver\Server;
+use MongoDB\Exception\InvalidArgumentException;
+use MongoDB\Exception\InvalidArgumentTypeException;
+use MongoDB\Exception\RuntimeException;
+use MongoDB\Exception\UnexpectedValueException;
+
+/**
+ * Stream wrapper for reading and writing a GridFS file.
+ *
+ * @internal
+ * @see MongoDB\GridFS\Bucket::openUploadStream()
+ */
+class StreamWrapper
+{
+    public $context;
+
+    private $bucket;
+    private $filename;
+    private $options;
+
+    private $protocol = 'gridfs';
+
+    private $at;
+    private $hashContext;
+
+    /**
+     * Constructs a writable upload stream.
+     *
+     * Supported options:
+     *
+     *  * chunkSizeBytes (integer): The number of bytes per chunk of this file.
+     *    Defaults to the chunkSizeBytes of the Bucket.
+     *
+     *  * metadata (document): User data for the "metadata" field of the files
+     *    collection document.
+     *
+     * The following options are deprecated:
+     *
+     *  * aliases (string[]): An array of aliases (i.e. filenames). Applications
+     *    wishing to store aliases should add an aliases field to the metadata
+     *    document instead.
+     *
+     *  * contentType (string): A valid MIME type. Applications wishing to store
+     *    a contentType should add a contentType field to the metadata document
+     *    instead.
+     *
+     * @param Bucket $bucket   Database name
+     * @param string $filename Filename
+     * @param array  $options  Upload options
+     * @throws InvalidArgumentException
+     */
+    public function __construct(Bucket $bucket, $filename, array $options = [])
+    {
+        $options += [
+            'chunkSizeBytes' => $bucket->getChunkSizeBytes(),
+        ];
+
+        if (isset($options['chunkSizeBytes']) && ! is_integer($options['chunkSizeBytes'])) {
+            throw new InvalidArgumentTypeException('"chunkSizeBytes" option', $options['chunkSizeBytes'], 'integer');
+        }
+
+        if (isset($options['metadata']) && ! is_array($options['metadata']) && ! is_object($options['metadata'])) {
+            throw new InvalidArgumentTypeException('"metadata" option', $options['metadata'], 'array or object');
+        }
+
+        if (isset($options['aliases'])) {
+            if ( ! is_array($options['aliases'])) {
+                throw new InvalidArgumentTypeException('"aliases" option', $options['aliases'], 'array or object');
+            }
+
+            $expectedIndex = 0;
+
+            foreach ($options['aliases'] as $i => $alias) {
+                if ($i !== $expectedIndex) {
+                    throw new InvalidArgumentException(sprintf('"aliases" option is not a list (unexpected index: "%s")', $i));
+                }
+
+                if ( ! is_string($alias)) {
+                    throw new InvalidArgumentTypeException(sprintf('$options["aliases"][%d]', $i), $alias, 'string');
+                }
+
+                $expectedIndex += 1;
+            }
+        }
+
+        if (isset($options['contentType']) && ! is_string($options['contentType'])) {
+            throw new InvalidArgumentTypeException('"contentType" option', $options['contentType'], 'string');
+        }
+
+        $this->bucket = $bucket;
+        $this->filename = (string) $filename;
+        $this->options = $options;
+        $this->hashContext = hash_init('md5');
+    }
+
+    public function stream_write($data)
+    {
+        hash_update($this->hashContext, $data);
+
+        //fopen('php://memory', )
+    }
+
+    /**
+     * Register the GridFS stream wrapper.
+     *
+     * @param Manager $manager  Manager instance from the driver
+     * @param string  $protocol Protocol to register
+     */
+    public static function register(Manager $manager, $protocol = 'gridfs')
+    {
+        if (in_array($protocol, stream_get_wrappers())) {
+            stream_wrapper_unregister($protocol);
+        }
+
+        // Set the client passed in as the default stream context client
+        stream_wrapper_register($protocol, get_called_class(), STREAM_IS_URL);
+        $default = stream_context_get_options(stream_context_get_default());
+        $default[$protocol]['manager'] = $manager;
+        stream_context_set_default($default);
+    }
+
+    public function stream_open($path, $mode, $options, &$openedPath)
+    {
+        $this->initProtocol($path);
+        $this->params = $this->getDatabase($path);
+        $this->mode = rtrim($mode, 'bt');
+
+        if ($errors = $this->validate($path, $this->mode)) {
+            return $this->triggerError($errors);
+        }
+
+        return $this->boolCall(function() use ($path) {
+            switch ($this->mode) {
+                case 'r': return $this->openReadStream($path);
+                case 'a': return $this->openAppendStream($path);
+                default: return $this->openWriteStream($path);
+            }
+        });
+    }
+
+    private function validate($path, $mode)
+    {
+        $errors = [];
+
+        if (!in_array($mode, ['r', 'w', 'a', 'x'])) {
+            $errors[] = "Mode not supported: {$mode}. "
+                . "Use one 'r', 'w', 'a', or 'x'.";
+        }
+
+        return $errors;
+    }
+
+    /**
+     * Trigger one or more errors
+     *
+     * @param string|array $errors Errors to trigger
+     * @param mixed        $flags  If set to STREAM_URL_STAT_QUIET, then no
+     *                             error or exception occurs
+     *
+     * @return bool Returns false
+     * @throws \RuntimeException if throw_errors is true
+     */
+    private function triggerError($errors, $flags = null)
+    {
+        // This is triggered with things like file_exists()
+        if ($flags & STREAM_URL_STAT_QUIET) {
+            return $flags & STREAM_URL_STAT_LINK
+                // This is triggered for things like is_link()
+                ? $this->formatUrlStat(false)
+                : false;
+        }
+        // This is triggered when doing things like lstat() or stat()
+        trigger_error(implode("\n", (array) $errors), E_USER_WARNING);
+        return false;
+    }
+}
diff --git a/src/GridFS/Upload.php b/src/GridFS/Upload.php
new file mode 100644
index 000000000..c10ca287b
--- /dev/null
+++ b/src/GridFS/Upload.php
@@ -0,0 +1,102 @@
+<?php
+
+namespace MongoDB\GridFS;
+
+use MongoDB\Driver\Server;
+use MongoDB\Exception\InvalidArgumentException;
+use MongoDB\Exception\InvalidArgumentTypeException;
+use MongoDB\Exception\RuntimeException;
+use MongoDB\Exception\UnexpectedValueException;
+
+/**
+ * Writable stream for uploading a file to GridFS.
+ *
+ * @internal
+ * @see MongoDB\GridFS\Bucket::openUploadStream()
+ */
+class Upload
+{
+    private $bucket;
+    private $filename;
+    private $options;
+
+    private $at;
+    private $hashContext;
+
+    /**
+     * Constructs a writable upload stream.
+     *
+     * Supported options:
+     *
+     *  * chunkSizeBytes (integer): The number of bytes per chunk of this file.
+     *    Defaults to the chunkSizeBytes of the Bucket.
+     *
+     *  * metadata (document): User data for the "metadata" field of the files
+     *    collection document.
+     *
+     * The following options are deprecated:
+     *
+     *  * aliases (string[]): An array of aliases (i.e. filenames). Applications
+     *    wishing to store aliases should add an aliases field to the metadata
+     *    document instead.
+     *
+     *  * contentType (string): A valid MIME type. Applications wishing to store
+     *    a contentType should add a contentType field to the metadata document
+     *    instead.
+     *
+     * @param Bucket $bucket   Database name
+     * @param string $filename Filename
+     * @param array  $options  Upload options
+     * @throws InvalidArgumentException
+     */
+    public function __construct(Bucket $bucket, $filename, array $options = [])
+    {
+        $options += [
+            'chunkSizeBytes' => $bucket->getChunkSizeBytes(),
+        ];
+
+        if (isset($options['chunkSizeBytes']) && ! is_integer($options['chunkSizeBytes'])) {
+            throw new InvalidArgumentTypeException('"chunkSizeBytes" option', $options['chunkSizeBytes'], 'integer');
+        }
+
+        if (isset($options['metadata']) && ! is_array($options['metadata']) && ! is_object($options['metadata'])) {
+            throw new InvalidArgumentTypeException('"metadata" option', $options['metadata'], 'array or object');
+        }
+
+        if (isset($options['aliases'])) {
+            if ( ! is_array($options['aliases'])) {
+                throw new InvalidArgumentTypeException('"aliases" option', $options['aliases'], 'array or object');
+            }
+
+            $expectedIndex = 0;
+
+            foreach ($options['aliases'] as $i => $alias) {
+                if ($i !== $expectedIndex) {
+                    throw new InvalidArgumentException(sprintf('"aliases" option is not a list (unexpected index: "%s")', $i));
+                }
+
+                if ( ! is_string($alias)) {
+                    throw new InvalidArgumentTypeException(sprintf('$options["aliases"][%d]', $i), $alias, 'string');
+                }
+
+                $expectedIndex += 1;
+            }
+        }
+
+        if (isset($options['contentType']) && ! is_string($options['contentType'])) {
+            throw new InvalidArgumentTypeException('"contentType" option', $options['contentType'], 'string');
+        }
+
+        $this->bucket = $bucket;
+        $this->filename = (string) $filename;
+        $this->options = $options;
+        $this->hashContext = hash_init('md5');
+    }
+
+    function write($data)
+    {
+        hash_update($this->hashContext, $data);
+
+        fopen('php://memory', )
+    }
+}