This article is from the Calendars FAQ, by Claus Tondering email@example.com with numerous contributions by others.
The Bible clearly makes Saturday (the Sabbath) the last day of the
week. Therefore it is common Jewish and Christian practice to regard
Sunday as the first day of the week (as is also evident from the
Portuguese names for the week days mentioned in section 6.2). However,
the fact that, for example, Russian uses the name "second" for
Tuesday, indicates that some nations regard Monday as the first day.
In international standard ISO-8601 the International Organization for
Standardization has decreed that Monday shall be the first day of the