Класс Неделя библиотеки Time Period для .NET включает поддержку формата недели ISO 8601:
public void CalendarWeekSample()
{
DateTime testDate = new DateTime( 2007, 12, 31 );
// .NET calendar week
TimeCalendar calendar = new TimeCalendar();
Console.WriteLine( "Calendar Week of {0}: {1}", testDate.ToShortDateString(),
new Week( testDate, calendar ).WeekOfYear );
// > Calendar Week of 31.12.2007: 53
// ISO 8601 calendar week
TimeCalendar calendarIso8601 = new TimeCalendar(
new TimeCalendarConfig { YearWeekType = YearWeekType.Iso8601 } );
Console.WriteLine( "ISO 8601 Week of {0}: {1}", testDate.ToShortDateString(),
new Week( testDate, calendarIso8601 ).WeekOfYear );
// > ISO 8601 Week of 31.12.2007: 1
} // CalendarWeekSample