diff --git a/bin/polyserve b/bin/polyserve
index 87c1aab36..ac5606557 100755
--- a/bin/polyserve
+++ b/bin/polyserve
@@ -9,8 +9,10 @@
  * subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
  */
 
-var resolve = require('resolve');
-var argv = require('minimist')(process.argv);
+'use strict';
+
+const resolve = require('resolve');
+const argv = require('minimist')(process.argv);
 
 process.title = 'polyserve';
 
@@ -26,11 +28,13 @@ if (argv.h || argv.help) {
 }
 
 resolve('polyserve', {basedir: process.cwd()}, function(error, path) {
-  var polyserve = path ? require(path) : require('..');
+  let polyserve = path ? require(path) : require('..');
   polyserve.startServer({
     port: argv.p,
     page: argv.o,
     host: argv.H,
     browser: argv.b
+  }).catch((e) => {
+    process.exit(69);
   });
 });
diff --git a/src/bower_config.js b/src/bower_config.js
index 4c732ac6d..70d83e946 100644
--- a/src/bower_config.js
+++ b/src/bower_config.js
@@ -8,16 +8,17 @@
  * subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
  */
 
-var path = require('path');
-var fs = require('fs');
+'use strict';
+
+const path = require('path');
+const fs = require('fs');
 
 function bowerConfigPath(root) {
-  root = path.join(process.cwd(), root || '.');
   return path.resolve(root, 'bower.json');
 }
 
 function bowerConfigContents(root) {
-  var contents;
+  let contents;
 
   try {
     contents = fs.readFileSync(bowerConfigPath(root));
diff --git a/src/make_app.js b/src/make_app.js
index 30d7b205d..6542a7647 100644
--- a/src/make_app.js
+++ b/src/make_app.js
@@ -8,34 +8,40 @@
  * subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
  */
 
-var express = require('express');
-var fs = require('fs');
-var path = require('path');
-var parseUrl = require('url').parse;
-var send = require('send');
-var bowerConfig = require('./bower_config');
+'use strict';
+
+const express = require('express');
+const fs = require('fs');
+const path = require('path');
+const parseUrl = require('url').parse;
+const send = require('send');
+const bowerConfig = require('./bower_config');
 
 /**
  * Make a polyserve express app.
- * @param  {string} componentDir The directory to serve components from.
- * @param  {string} packageName  A name for this polyserve package.
- * @param  {Object} headers      An object keyed by header name containing
- *                               header values.
- * @param  {string} root         The root directory to serve a package from
- * @return {Object}              An express app which can be served with
- *                               `app.get`
+ * @param  {Object} options
+ * @param  {string} options.componentDir The directory to serve components from.
+ * @param  {string} options.packageName A name for this polyserve package.
+ * @param  {Object} options.headers An object keyed by header name containing
+ *         header values.
+ * @param  {string} options.root The root directory to serve a package from
+ * @return {Object} An express app which can be served with `app.get`
  */
-function makeApp(componentDir, packageName, headers, root) {
-  componentDir = componentDir || 'bower_components';
-  packageName = packageName || bowerConfig(root).name;
-  root = root || '.';
+function makeApp(options) {
+
+  let root = options.root;
+  let componentDir = options.componentDir || 'bower_components';
+  let packageName = options.packageName || bowerConfig(root).name
+      || path.basename(process.cwd());
+  let headers = options.headers || {};
 
-  var app = express();
+  let app = express();
 
   app.get('*', function (req, res) {
     // Serve local files from . and other components from bower_components
-    var url = parseUrl(req.url, true);
-    var splitPath = url.pathname.split('/').slice(1);
+    let url = parseUrl(req.url, true);
+    let splitPath = url.pathname.split('/').slice(1);
+
     if (splitPath[0] === packageName) {
       if (root) {
         splitPath = [root].concat(splitPath.slice(1));
@@ -45,9 +51,11 @@ function makeApp(componentDir, packageName, headers, root) {
     } else {
       splitPath = [componentDir].concat(splitPath);
     }
-    var filePath = splitPath.join('/');
+    let filePath = splitPath.join('/');
+    console.log('filePath', filePath);
+
     if (headers) {
-      for (header in headers) {
+      for (let header in headers) {
         res.append(header, headers[header]);
       }
     }
diff --git a/src/start_server.js b/src/start_server.js
index e921a61d4..fe3bf5a80 100644
--- a/src/start_server.js
+++ b/src/start_server.js
@@ -8,31 +8,42 @@
  * subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
  */
 
-var express = require('express');
-var http = require('http');
-var makeApp = require('./make_app');
-var opn = require('opn');
-var util = require('util');
-var findPort = require('find-port');
+'use strict';
 
+const express = require('express');
+const findPort = require('find-port');
+const http = require('http');
+const makeApp = require('./make_app');
+const opn = require('opn');
+
+/**
+ * @return {Promise} A Promise that completes when the server has started.
+ */
 function startServer(options) {
-  if (!options.port) {
-    findPort(8080, 8180, function(ports) {
-      options.port = ports[0];
-      startWithPort(options);
-    });
-  }
-  else {
-    startWithPort(options);
-  }
+  return new Promise((resolve, reject) => {
+    if (options.port) {
+      resolve(options);
+    } else {
+      findPort(8080, 8180, function(ports) {
+        options.port = ports[0];
+        resolve(options);
+      });
+    }
+  }).then((opts) => startWithPort(opts));
 }
 
+let portInUseMessage = (port) => `
+ERROR: Port in use: ${port}
+Please choose another port, or let an unused port be chosen automatically.
+`;
+
 /**
  * @param {Object} options
  * @param {Number} options.port -- port number
  * @param {String} options.host -- hostname string
  * @param {String=} options.page -- page path, ex: "/", "/index.html"
  * @param {(String|String[])} options.browser -- names of browser apps to launch
+ * @return {Promise}
  */
 function startWithPort(options) {
 
@@ -41,36 +52,48 @@ function startWithPort(options) {
 
   console.log('Starting Polyserve on port ' + options.port);
 
-  var app = express();
-  var polyserve = makeApp(options.componentDir, options.packageName);
+  let app = express();
+  let polyserve = makeApp({
+    componentDir: options.componentDir,
+    packageName: options.packageName,
+    root: process.cwd(),
+  });
 
   app.use('/components/', polyserve);
 
-  var server = http.createServer(app);
+  let server = http.createServer(app);
+  let serverStartedResolve;
+  let serverStartedReject;
+  let serverStartedPromise = new Promise((resolve, reject) => {
+    serverStartedResolve = resolve;
+    serverStartedReject = reject;
+  });
 
-  server = app.listen(options.port, options.host);
+  server = app.listen(options.port, options.host,
+      () => serverStartedResolve(server));
 
   server.on('error', function(err) {
-    if (err.code === 'EADDRINUSE')
-      console.error("ERROR: Port in use", options.port,
-        "\nPlease choose another port, or let an unused port be chosen automatically.");
-    process.exit(69);
+    if (err.code === 'EADDRINUSE') {
+      console.error(portInUseMessage(options.port));
+    }
+    serverStartedReject(err);
   });
 
-  var baseUrl = util.format('http://'+ options.host +':%d/components/%s/', options.port,
-    polyserve.packageName);
-  console.log('Files in this directory are available under ' + baseUrl);
+  let baseUrl = `http://${options.host}:${options.port}/components/${polyserve.packageName}/`;
+  console.log(`Files in this directory are available under ${baseUrl}`);
 
   if (options.page) {
-    var url = baseUrl + (options.page === true ? 'index.html' : options.page);
+    let url = baseUrl + (options.page === true ? 'index.html' : options.page);
     if (Array.isArray(options.browser)) {
-      for (var i = 0; i < options.browser.length; i++)
+      for (let i = 0; i < options.browser.length; i++)
         opn(url, options.browser[i]);
     }
     else {
       opn(url, options.browser);
     }
   }
+
+  return serverStartedPromise;
 }
 
 module.exports = startServer;