diff --git a/README.md b/README.md
index c2d6eac..51c8904 100644
--- a/README.md
+++ b/README.md
@@ -243,6 +243,28 @@ polyglot.t("car", 2);
 => "2 cars"
 ```
 
+If you pass a `numberFormat` _function_ to the constructor, Polyglot will use
+it to translate interpolated `Number`s to `String`s. That's useful because
+different locales have different rules for formatting numbers: `2,000.56` in
+English versus `1 234,56` in French, for instance.
+
+```js
+polyglot = new Polyglot({
+  phrases: { num_cars: '%{smart_count} car |||| %{smart_count} cars' },
+  numberFormat: new Intl.NumberFormat('en').format // Chrome, Firefox, IE11+, Node 0.12+ with ICU
+})
+polyglot.t("num_cars", 2000); // internally, calls options.numberFormat.format(2000)
+=> "2,000 cars"
+```
+
+(A primer on [Intl.NumberFormat](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/NumberFormat)
+in Node: Node 0.12+ comes with Intl as long as it's compiled with ICU (which is
+the default). By default, the only locale Node supports is en-US. You can add
+[full-icu](https://www.npmjs.com/package/full-icu) to your project to support
+other locales. Finally, Polyglot accepts a _function_, not an Intl.NumberFormat
+instance: if you have a NumberFormat instance, pass its `.format` property to
+Polyglot.
+
 If you like, you can provide a default value in case the phrase is missing.
 Use the special option key "_" to specify a default.
 
diff --git a/index.js b/index.js
index 84e53a8..576eee9 100644
--- a/index.js
+++ b/index.js
@@ -119,7 +119,7 @@ var tokenRegex = /%\{(.*?)\}/g;
 //
 // You should pass in a third argument, the locale, to specify the correct plural type.
 // It defaults to `'en'` with 2 plural forms.
-function transformPhrase(phrase, substitutions, locale) {
+function transformPhrase(phrase, substitutions, locale, numberFormat) {
   if (typeof phrase !== 'string') {
     throw new TypeError('Polyglot.transformPhrase expects argument #1 to be string');
   }
@@ -144,8 +144,14 @@ function transformPhrase(phrase, substitutions, locale) {
   // Interpolate: Creates a `RegExp` object for each interpolation placeholder.
   result = result.replace(tokenRegex, function (expression, argument) {
     if (!has(options, argument)) { return ''; }
+
+    var replacement = options[argument];
+    if (typeof replacement === 'number') {
+      replacement = numberFormat(replacement);
+    }
+
     // Ensure replacement value is escaped to prevent special $-prefixed regex replace tokens.
-    return replace.call(options[argument], dollarRegex, dollarBillsYall);
+    return replace.call(replacement, dollarRegex, dollarBillsYall);
   });
 
   return result;
@@ -157,6 +163,7 @@ function Polyglot(options) {
   this.phrases = {};
   this.extend(opts.phrases || {});
   this.currentLocale = opts.locale || 'en';
+  this.numberFormat = opts.numberFormat || String;
   this.allowMissing = !!opts.allowMissing;
   this.warn = opts.warn || warn;
 }
@@ -165,7 +172,9 @@ function Polyglot(options) {
 //
 // Get or set locale. Internally, Polyglot only uses locale for pluralization.
 Polyglot.prototype.locale = function (newLocale) {
-  if (newLocale) this.currentLocale = newLocale;
+  if (newLocale) {
+    this.currentLocale = newLocale;
+  }
   return this.currentLocale;
 };
 
@@ -314,7 +323,7 @@ Polyglot.prototype.t = function (key, options) {
     result = key;
   }
   if (typeof phrase === 'string') {
-    result = transformPhrase(phrase, opts, this.currentLocale);
+    result = transformPhrase(phrase, opts, this.currentLocale, this.numberFormat);
   }
   return result;
 };
diff --git a/test/index.js b/test/index.js
index 055ff1e..ca9bf96 100644
--- a/test/index.js
+++ b/test/index.js
@@ -8,7 +8,8 @@ describe('t', function () {
     hello: 'Hello',
     hi_name_welcome_to_place: 'Hi, %{name}, welcome to %{place}!',
     name_your_name_is_name: '%{name}, your name is %{name}!',
-    empty_string: ''
+    empty_string: '',
+    number: '%{number}'
   };
 
   var polyglot;
@@ -89,6 +90,16 @@ describe('t', function () {
     expect(instance.t('nav.cta.join_now')).to.equal('Join now!');
     expect(instance.t('header.sign_in')).to.equal('Sign In');
   });
+
+  it('uses numberFormat', function () {
+    var instance = new Polyglot({
+      phrases: phrases,
+      // prove we're passed a Number by doing math on it and formatting it
+      numberFormat: function (n) { return 'x' + (n + 2); }
+    });
+
+    expect(instance.t('number', { number: 1234.56 })).to.equal('x1236.56');
+  });
 });
 
 describe('pluralize', function () {