diff --git a/packages/metro-bundler/src/HmrServer/getBundlingOptionsForHmr.js b/packages/metro-bundler/src/HmrServer/getBundlingOptionsForHmr.js
new file mode 100644
index 00000000..a1a2571a
--- /dev/null
+++ b/packages/metro-bundler/src/HmrServer/getBundlingOptionsForHmr.js
@@ -0,0 +1,52 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @format
+ * @flow
+ */
+
+'use strict';
+
+import type {Options as BundleOptions} from '../DeltaBundler';
+
+/**
+ * Module to easily create the needed configuration parameters needed for the
+ * bundler for HMR (since a lot of params are not relevant in this use case).
+ */
+module.exports = function getBundlingOptionsForHmr(
+  entryFile: string,
+  platform: string,
+): BundleOptions {
+  // These are the really meaningful bundling options. The others below are
+  // not relevant for HMR.
+  const mainOptions = {
+    deltaBundleId: null,
+    entryFile,
+    hot: true,
+    minify: false,
+    platform,
+    wrapModules: false,
+  };
+
+  return {
+    ...mainOptions,
+    assetPlugins: [],
+    dev: true,
+    entryModuleOnly: false,
+    excludeSource: false,
+    generateSourceMaps: false,
+    inlineSourceMap: false,
+    isolateModuleIDs: false,
+    onProgress: null,
+    resolutionResponse: null,
+    runBeforeMainModule: [],
+    runModule: false,
+    sourceMapUrl: '',
+    unbundle: false,
+  };
+};
diff --git a/packages/metro-bundler/src/HmrServer/index.js b/packages/metro-bundler/src/HmrServer/index.js
new file mode 100644
index 00000000..60ee3eb3
--- /dev/null
+++ b/packages/metro-bundler/src/HmrServer/index.js
@@ -0,0 +1,114 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @format
+ * @flow
+ */
+
+'use strict';
+
+const getBundlingOptionsForHmr = require('./getBundlingOptionsForHmr');
+const querystring = require('querystring');
+const url = require('url');
+
+import type DeltaTransformer from '../DeltaBundler/DeltaTransformer';
+import type PackagerServer from '../Server';
+import type {Reporter} from '../lib/reporting';
+
+type Client = {|
+  deltaTransformer: DeltaTransformer,
+  sendFn: (data: string) => mixed,
+|};
+
+/**
+ * The HmrServer (Hot Module Reloading) implements a lightweight interface
+ * to communicate easily to the logic in the React Native repository (which
+ * is the one that handles the Web Socket connections).
+ *
+ * This interface allows the HmrServer to hook its own logic to WS clients
+ * getting connected, disconnected or having errors (through the
+ * `onClientConnect`, `onClientDisconnect` and `onClientError` methods).
+ */
+class HmrServer<TClient: Client> {
+  _packagerServer: PackagerServer;
+  _reporter: Reporter;
+
+  constructor(packagerServer: PackagerServer, reporter: Reporter) {
+    this._packagerServer = packagerServer;
+    this._reporter = reporter;
+  }
+
+  async onClientConnect(
+    clientUrl: string,
+    sendFn: (data: string) => mixed,
+  ): Promise<Client> {
+    const {bundleEntry, platform} = querystring.parse(
+      /* $FlowFixMe: url might be null */
+      url.parse(clientUrl).query,
+    );
+
+    // Create a new DeltaTransformer for each client. Once the clients are
+    // modified to support Delta Bundles, they'll be able to pass the
+    // DeltaBundleId param through the WS connection and we'll be able to share
+    // the same DeltaTransformer between the WS connection and the HTTP one.
+    const deltaBundler = this._packagerServer.getDeltaBundler();
+    const {deltaTransformer} = await deltaBundler.getDeltaTransformer(
+      getBundlingOptionsForHmr(bundleEntry, platform),
+    );
+
+    // Trigger an initial build to start up the DeltaTransformer.
+    await deltaTransformer.getDelta();
+
+    // Listen to file changes.
+    const client = {sendFn, deltaTransformer};
+    deltaTransformer.on('change', this._handleFileChange.bind(this, client));
+
+    return client;
+  }
+
+  onClientError(client: TClient, e: Error) {
+    this._reporter.update({
+      type: 'hmr_client_error',
+      error: e,
+    });
+    this.onClientDisconnect(client);
+  }
+
+  onClientDisconnect(client: TClient) {
+    // We can safely remove all listeners from the delta transformer since the
+    // transformer is not shared between clients.
+    client.deltaTransformer.removeAllListeners('change');
+  }
+
+  async _handleFileChange(client: Client) {
+    client.sendFn(JSON.stringify({type: 'update-start'}));
+    client.sendFn(JSON.stringify(await this._prepareResponse(client)));
+    client.sendFn(JSON.stringify({type: 'update-done'}));
+  }
+
+  async _prepareResponse(client: Client): Promise<{type: string, body: {}}> {
+    const result = await client.deltaTransformer.getDelta();
+    const modules = [];
+
+    for (const id in result.delta) {
+      modules.push({id, code: result.delta[id]});
+    }
+
+    return {
+      type: 'update',
+      body: {
+        modules,
+        inverseDependencies: result.inverseDependencies,
+        sourceURLs: {},
+        sourceMappingURLs: {}, // TODO: handle Source Maps
+      },
+    };
+  }
+}
+
+module.exports = HmrServer;
diff --git a/packages/metro-bundler/src/lib/TerminalReporter.js b/packages/metro-bundler/src/lib/TerminalReporter.js
index 3c73ded4..ce7daa40 100644
--- a/packages/metro-bundler/src/lib/TerminalReporter.js
+++ b/packages/metro-bundler/src/lib/TerminalReporter.js
@@ -251,6 +251,9 @@ class TerminalReporter {
       case 'worker_stderr_chunk':
         this._logWorkerChunk('stderr', event.chunk);
         break;
+      case 'hmr_client_error':
+        this._logHmrClientError(event.error);
+        break;
     }
   }
 
@@ -396,6 +399,15 @@ class TerminalReporter {
       .join('\n');
   }
 
+  _logHmrClientError(e: Error): void {
+    reporting.logError(
+      this.terminal,
+      'A WebSocket client got a connection error. Please reload your device ' +
+        'to get HMR working again: %s',
+      e,
+    );
+  }
+
   /**
    * Single entry point for reporting events. That allows us to implement the
    * corresponding JSON reporter easily and have a consistent reporting.
diff --git a/packages/metro-bundler/src/lib/reporting.js b/packages/metro-bundler/src/lib/reporting.js
index ddbc96be..e1f339cc 100644
--- a/packages/metro-bundler/src/lib/reporting.js
+++ b/packages/metro-bundler/src/lib/reporting.js
@@ -85,6 +85,10 @@ export type ReportableEvent =
   | {
       type: 'worker_stderr_chunk',
       chunk: string,
+    }
+  | {
+      type: 'hmr_client_error',
+      error: Error,
     };
 
 /**