diff --git a/chrono/datetime.cpp b/chrono/datetime.cpp
index 41f5c85..b75820f 100644
--- a/chrono/datetime.cpp
+++ b/chrono/datetime.cpp
@@ -196,8 +196,53 @@ std::pair<DateTime, TimeSpan> DateTime::fromIsoString(const char *str)
  */
 void DateTime::toString(string &result, DateTimeOutputFormat format, bool noMilliseconds) const
 {
+    if (format == DateTimeOutputFormat::Iso) {
+        result = toIsoString();
+        return;
+    }
+
     stringstream s(stringstream::in | stringstream::out);
     s << setfill('0');
+
+    if (format == DateTimeOutputFormat::IsoOmittingDefaultComponents) {
+        constexpr auto dateDelimiter = '-', timeDelimiter = ':';
+        const int components[] = { year(), month(), day(), hour(), minute(), second(), millisecond(), microsecond(), nanosecond() };
+        const int *const firstTimeComponent = components + 3;
+        const int *const firstFractionalComponent = components + 6;
+        const int *const lastComponent = components + 8;
+        const int *componentsEnd = noMilliseconds ? firstFractionalComponent : lastComponent + 1;
+        for (const int *i = componentsEnd - 1; i > components; --i) {
+            if (i >= firstTimeComponent && *i == 0) {
+                componentsEnd = i;
+            } else if (i < firstTimeComponent && *i == 1) {
+                componentsEnd = i;
+            }
+        }
+        for (const int *i = components; i != componentsEnd; ++i) {
+            if (i == firstTimeComponent) {
+                s << 'T';
+            } else if (i == firstFractionalComponent) {
+                s << '.';
+            }
+            if (i == components) {
+                s << setw(4) << *i;
+            } else if (i < firstFractionalComponent) {
+                if (i < firstTimeComponent) {
+                    s << dateDelimiter;
+                } else if (i > firstTimeComponent) {
+                    s << timeDelimiter;
+                }
+                s << setw(2) << *i;
+            } else if (i < lastComponent) {
+                s << setw(3) << *i;
+            } else {
+                s << *i / TimeSpan::nanosecondsPerTick;
+            }
+        }
+        result = s.str();
+        return;
+    }
+
     if (format == DateTimeOutputFormat::DateTimeAndWeekday || format == DateTimeOutputFormat::DateTimeAndShortWeekday)
         s << printDayOfWeek(dayOfWeek(), format == DateTimeOutputFormat::DateTimeAndShortWeekday) << ' ';
     if (format == DateTimeOutputFormat::DateOnly || format == DateTimeOutputFormat::DateAndTime || format == DateTimeOutputFormat::DateTimeAndWeekday
diff --git a/chrono/datetime.h b/chrono/datetime.h
index 319f8e1..e3173f6 100644
--- a/chrono/datetime.h
+++ b/chrono/datetime.h
@@ -19,7 +19,9 @@ enum class DateTimeOutputFormat {
     DateOnly, /**< date only */
     TimeOnly, /**< time only */
     DateTimeAndWeekday, /**< date with weekday and time */
-    DateTimeAndShortWeekday /**< date with abbreviated weekday and time */
+    DateTimeAndShortWeekday, /**< date with abbreviated weekday and time */
+    Iso, /**< ISO format like DateTime::toIsoString() */
+    IsoOmittingDefaultComponents, /**< ISO format like DateTime::toIsoString() omitting default components, e.g. just "2017" instead of "2017-01-01T00:00:00" */
 };
 
 /*!
diff --git a/tests/chronotests.cpp b/tests/chronotests.cpp
index 65a9028..3b67616 100644
--- a/tests/chronotests.cpp
+++ b/tests/chronotests.cpp
@@ -187,6 +187,23 @@ void ChronoTests::testDateTime()
     CPPUNIT_ASSERT_THROW_MESSAGE("invalid .", DateTime::fromIsoString("2017-08.5-23T19:40:15.985077682+02:00"), ConversionException);
     CPPUNIT_ASSERT_THROW_MESSAGE("invalid :", DateTime::fromIsoString("2017:08-23T19:40:15.985077682+02:00"), ConversionException);
     CPPUNIT_ASSERT_THROW_MESSAGE("invalid :", DateTime::fromIsoString("2017-08-23T19:40:15:985077682+02:00"), ConversionException);
+    // ISO string via toString() format option
+    CPPUNIT_ASSERT_EQUAL("1234-05-06T07:08:09.0105005"s, DateTime::fromDateAndTime(1234, 5, 6, 7, 8, 9, 10.5005).toString(DateTimeOutputFormat::Iso));
+    CPPUNIT_ASSERT_EQUAL("1234-05-06T07:08:09.0105005"s,
+        DateTime::fromDateAndTime(1234, 5, 6, 7, 8, 9, 10.5005).toString(DateTimeOutputFormat::IsoOmittingDefaultComponents));
+    CPPUNIT_ASSERT_EQUAL("1234-05-06T07:08:09.010500"s,
+        DateTime::fromDateAndTime(1234, 5, 6, 7, 8, 9, 10.500).toString(DateTimeOutputFormat::IsoOmittingDefaultComponents));
+    CPPUNIT_ASSERT_EQUAL(
+        "1234-05-06T07:08:09.010"s, DateTime::fromDateAndTime(1234, 5, 6, 7, 8, 9, 10).toString(DateTimeOutputFormat::IsoOmittingDefaultComponents));
+    CPPUNIT_ASSERT_EQUAL(
+        "1234-05-06T07:08:09"s, DateTime::fromDateAndTime(1234, 5, 6, 7, 8, 9).toString(DateTimeOutputFormat::IsoOmittingDefaultComponents));
+    CPPUNIT_ASSERT_EQUAL(
+        "1234-05-06T07:08"s, DateTime::fromDateAndTime(1234, 5, 6, 7, 8).toString(DateTimeOutputFormat::IsoOmittingDefaultComponents));
+    CPPUNIT_ASSERT_EQUAL("1234-05-06T07"s, DateTime::fromDateAndTime(1234, 5, 6, 7).toString(DateTimeOutputFormat::IsoOmittingDefaultComponents));
+    CPPUNIT_ASSERT_EQUAL("1234-05-06"s, DateTime::fromDateAndTime(1234, 5, 6).toString(DateTimeOutputFormat::IsoOmittingDefaultComponents));
+    CPPUNIT_ASSERT_EQUAL("1234-05"s, DateTime::fromDateAndTime(1234, 5).toString(DateTimeOutputFormat::IsoOmittingDefaultComponents));
+    CPPUNIT_ASSERT_EQUAL("1234"s, DateTime::fromDateAndTime(1234).toString(DateTimeOutputFormat::IsoOmittingDefaultComponents));
+    CPPUNIT_ASSERT_EQUAL("0001"s, DateTime().toString(DateTimeOutputFormat::IsoOmittingDefaultComponents));
 
 // test now() and exactNow() (or at least whether both behave the same)
 #if defined(PLATFORM_UNIX)