diff --git a/README.md b/README.md
index f2ea1f3..25b58da 100644
--- a/README.md
+++ b/README.md
@@ -118,6 +118,7 @@ Returns a new formatter for the given string *specifier*. The specifier string m
 * `%L` - milliseconds as a decimal number [000, 999].
 * `%p` - either AM or PM.*
 * `%S` - second as a decimal number [00,61].
+* `%u` - Monday-based (ISO) weekday as a decimal number [1,7].
 * `%U` - Sunday-based week of the year as a decimal number [00,53].
 * `%w` - Sunday-based weekday as a decimal number [0,6].
 * `%W` - Monday-based week of the year as a decimal number [00,53].
diff --git a/src/locale.js b/src/locale.js
index a03d6a2..4e6dce5 100644
--- a/src/locale.js
+++ b/src/locale.js
@@ -59,8 +59,9 @@ export default function formatLocale(locale) {
     "M": formatMinutes,
     "p": formatPeriod,
     "S": formatSeconds,
+    "u": formatWeekdayNumberMonday,
     "U": formatWeekNumberSunday,
-    "w": formatWeekdayNumber,
+    "w": formatWeekdayNumberSunday,
     "W": formatWeekNumberMonday,
     "x": null,
     "X": null,
@@ -86,8 +87,9 @@ export default function formatLocale(locale) {
     "M": formatUTCMinutes,
     "p": formatUTCPeriod,
     "S": formatUTCSeconds,
+    "u": formatUTCWeekdayNumberMonday,
     "U": formatUTCWeekNumberSunday,
-    "w": formatUTCWeekdayNumber,
+    "w": formatUTCWeekdayNumberSunday,
     "W": formatUTCWeekNumberMonday,
     "x": null,
     "X": null,
@@ -113,8 +115,9 @@ export default function formatLocale(locale) {
     "M": parseMinutes,
     "p": parsePeriod,
     "S": parseSeconds,
+    "u": parseWeekdayNumberMonday,
     "U": parseWeekNumberSunday,
-    "w": parseWeekdayNumber,
+    "w": parseWeekdayNumberSunday,
     "W": parseWeekNumberMonday,
     "x": parseLocaleDate,
     "X": parseLocaleTime,
@@ -171,7 +174,7 @@ export default function formatLocale(locale) {
 
       // Convert day-of-week and week-of-year to day-of-year.
       if ("W" in d || "U" in d) {
-        if (!("w" in d)) d.w = "W" in d ? 1 : 0;
+        if (!("w" in d)) d.w = "u" in d ? d.u % 7 : "W" in d ? 1 : 0;
         var day = "Z" in d ? utcDate(newYear(d.y)).getUTCDay() : newDate(newYear(d.y)).getDay();
         d.m = 0;
         d.d = "W" in d ? (d.w + 6) % 7 + d.W * 7 - (day + 5) % 7 : d.w + d.U * 7 - (day + 6) % 7;
@@ -339,11 +342,17 @@ function formatLookup(names) {
   return map;
 }
 
-function parseWeekdayNumber(d, string, i) {
+function parseWeekdayNumberSunday(d, string, i) {
   var n = numberRe.exec(string.slice(i, i + 1));
   return n ? (d.w = +n[0], i + n[0].length) : -1;
 }
 
+function parseWeekdayNumberMonday(d, string, i) {
+  var n = numberRe.exec(string.slice(i, i + 1));
+  var r = n ? (d.u = +n[0], i + n[0].length) : -1;
+  return r;
+}
+
 function parseWeekNumberSunday(d, string, i) {
   var n = numberRe.exec(string.slice(i));
   return n ? (d.U = +n[0], i + n[0].length) : -1;
@@ -441,11 +450,16 @@ function formatSeconds(d, p) {
   return pad(d.getSeconds(), p, 2);
 }
 
+function formatWeekdayNumberMonday(d) {
+  var dow = d.getDay();
+  return dow === 0 ? 7 : dow;
+}
+
 function formatWeekNumberSunday(d, p) {
   return pad(timeSunday.count(timeYear(d), d), p, 2);
 }
 
-function formatWeekdayNumber(d) {
+function formatWeekdayNumberSunday(d) {
   return d.getDay();
 }
 
@@ -500,11 +514,16 @@ function formatUTCSeconds(d, p) {
   return pad(d.getUTCSeconds(), p, 2);
 }
 
+function formatUTCWeekdayNumberMonday(d) {
+  var dow = d.getUTCDay();
+  return dow === 0 ? 7 : dow;
+}
+
 function formatUTCWeekNumberSunday(d, p) {
   return pad(utcSunday.count(utcYear(d), d), p, 2);
 }
 
-function formatUTCWeekdayNumber(d) {
+function formatUTCWeekdayNumberSunday(d) {
   return d.getUTCDay();
 }
 
diff --git a/test/format-test.js b/test/format-test.js
index cbf7460..0513a5b 100644
--- a/test/format-test.js
+++ b/test/format-test.js
@@ -191,6 +191,14 @@ tape("timeFormat(\"%L\")(date) formats zero-padded milliseconds", function(test)
   test.end();
 });
 
+tape("timeFormat(\"%u\")(date) formats week day numbers", function(test) {
+  var f = timeFormat.timeFormat("%u");
+  test.equal(f(date.local(1990,  0,  1,  0)), "1");
+  test.equal(f(date.local(1990,  0,  7,  0)), "7");
+  test.equal(f(date.local(2010,  2, 13, 23)), "6");
+  test.end();
+});
+
 tape("timeFormat(\"%U\")(date) formats zero-padded week numbers", function(test) {
   var f = timeFormat.timeFormat("%U");
   test.equal(f(date.local(1990,  0,  1,  0)), "00");
diff --git a/test/parse-test.js b/test/parse-test.js
index a7ee428..c4aefd7 100644
--- a/test/parse-test.js
+++ b/test/parse-test.js
@@ -57,7 +57,7 @@ tape("timeParse(\"%A %U %Y\")(date) parses weekday, week number (Sunday) and yea
   test.end();
 });
 
-tape("timeParse(\"%w %U %Y\")(date) parses numeric weekday, week number (Sunday) and year", function(test) {
+tape("timeParse(\"%w %U %Y\")(date) parses numeric weekday (Sunday), week number (Sunday) and year", function(test) {
   var p = timeFormat.timeParse("%w %U %Y");
   test.deepEqual(p("1 00 1990"), date.local(1990, 0, 1));
   test.deepEqual(p("0 05 1991"), date.local(1991, 1, 3));
@@ -66,6 +66,17 @@ tape("timeParse(\"%w %U %Y\")(date) parses numeric weekday, week number (Sunday)
   test.end();
 });
 
+tape("timeParse(\"%u %U %Y\")(date) parses numeric weekday (Monday), week number (Monday) and year", function(test) {
+  var p = timeFormat.timeParse("%u %W %Y");
+  test.deepEqual(p("1 00 1990"), date.local(1989, 11, 25));
+  test.deepEqual(p("1 01 1990"), date.local(1990, 0, 1));
+  test.deepEqual(p("1 05 1991"), date.local(1991, 1, 4));
+  test.deepEqual(p("7 00 1995"), date.local(1995, 0, 1));
+  test.deepEqual(p("1 01 1995"), date.local(1995, 0, 2));
+  test.equal(p("X 03 2010"), null);
+  test.end();
+});
+
 tape("timeParse(\"%W %Y\")(date) parses week number (Monday) and year", function(test) {
   var p = timeFormat.timeParse("%W %Y");
   test.deepEqual(p("01 1990"), date.local(1990,  0,  1));
@@ -92,7 +103,7 @@ tape("timeParse(\"%A %W %Y\")(date) parses weekday, week number (Monday) and yea
   test.end();
 });
 
-tape("timeParse(\"%w %W %Y\")(date) parses numeric weekday, week number (Monday) and year", function(test) {
+tape("timeParse(\"%w %W %Y\")(date) parses numeric weekday (Sunday), week number (Monday) and year", function(test) {
   var p = timeFormat.timeParse("%w %W %Y");
   test.deepEqual(p("1 01 1990"), date.local(1990, 0, 1));
   test.deepEqual(p("0 04 1991"), date.local(1991, 1, 3));
@@ -101,6 +112,15 @@ tape("timeParse(\"%w %W %Y\")(date) parses numeric weekday, week number (Monday)
   test.end();
 });
 
+tape("timeParse(\"%u %W %Y\")(date) parses numeric weekday (Monday), week number (Monday) and year", function(test) {
+  var p = timeFormat.timeParse("%u %W %Y");
+  test.deepEqual(p("1 01 1990"), date.local(1990, 0, 1));
+  test.deepEqual(p("7 04 1991"), date.local(1991, 1, 3));
+  test.deepEqual(p("7 00 1995"), date.local(1995, 0, 1));
+  test.equal(p("X 03 2010"), null);
+  test.end();
+});
+
 tape("timeParse(\"%m/%d/%y\")(date) parses month, date and two-digit year", function(test) {
   var p = timeFormat.timeParse("%m/%d/%y");
   test.deepEqual(p("02/03/69"), date.local(1969, 1, 3));
diff --git a/test/utcFormat-test.js b/test/utcFormat-test.js
index 5a01cf1..fd95a0c 100644
--- a/test/utcFormat-test.js
+++ b/test/utcFormat-test.js
@@ -179,6 +179,14 @@ tape("utcFormat(\"%L\")(date) formats zero-padded milliseconds", function(test)
   test.end();
 });
 
+tape("utcFormat(\"%u\")(date) formats week day numbers", function(test) {
+  var f = timeFormat.utcFormat("%u");
+  test.equal(f(date.utc(1990,  0,  1,  0)), "1");
+  test.equal(f(date.utc(1990,  0,  7,  0)), "7");
+  test.equal(f(date.utc(2010,  2, 13, 23)), "6");
+  test.end();
+});
+
 tape("utcFormat(\"%U\")(date) formats zero-padded week numbers", function(test) {
   var f = timeFormat.utcFormat("%U");
   test.equal(f(date.utc(1990,  0,  1,  0)), "00");