diff --git a/source/Ox/js/Format.js b/source/Ox/js/Format.js
index 77a66378..1b5a5cc9 100644
--- a/source/Ox/js/Format.js
+++ b/source/Ox/js/Format.js
@@ -639,6 +639,43 @@ Ox.formatDuration = function(seconds/*, decimals, format*/) {
     })).join(format == 'none' ? ':' : ' ');
 };
 
+/*
+Ox.formatISBN <f> Formats a string as an ISBN of a given length (10 or 13)
+    (isbn, length) -> <s> ISBN
+    isbn <s> ISBN
+    length <n> length (10 or 13)
+    > Ox.formatISBN('0-306-40615-2', 13)
+    '9780306406157'
+    > Ox.formatISBN('978-0-306-40615-7', 10)
+    '0306406152'
+*/
+Ox.formatISBN = function(isbn, length) {
+    var ret = '';
+    function getCheckDigit(isbn) {
+        var mod = isbn.length == 10 ? 11 : 10
+        return (mod - Ox.sum(
+            isbn.slice(0, -1).split('').map(function(digit, index) {
+                return isbn.length == 10
+                    ? parseInt(digit) * (10 - index)
+                    : parseInt(digit) * (index % 2 == 0 ? 1 : 3); 
+            })
+        ) % mod + '').replace('10', 'X');
+    }
+    isbn = isbn.toUpperCase().replace(/[^\dX]/g, '');
+    if ((
+        (isbn.length == 10 && isbn.slice(0, -1).indexOf('X') == -1)
+        || (isbn.length == 13 && isbn.slice(0, 3) == '978')
+    ) && isbn.slice(-1) == getCheckDigit(isbn)) {
+        if (isbn.length == length) {
+            ret = isbn
+        } else {
+            isbn = isbn.length == 10 ? '978' + isbn : isbn.slice(3);
+            ret = isbn.slice(0, -1) + getCheckDigit(isbn);
+        }
+    }
+    return ret;
+};
+
 /*@
 Ox.formatNumber <f> Formats a number with thousands separators
     (num, dec) -> <s> format number to string