But in many other cultures, Monday is held to be the first day of the week. For example, Monday is xingqi yi (???) in Chinese, meaning day one of the week. The international standard, ISO 8601, defines Monday as the first day of the week. Its name in Georgian, Greek and Syriac means “first day”. Quakers also traditionally refer to Monday as “First Day” eschewing the pagan origin of the English name “Monday”. For similar reasons the official liturgical calendar of the Roman Catholic Church refers to Monday as “Feria II”. (The Portuguese name for Monday reflects this, as do all the days’ names except Saturday and Sunday: the Portuguese word for Monday is segunda-feira.)
Modern culture usually looks at Monday as the beginning of the workweek, as it is typically Monday when adults go back to work and children back to school after the weekend. Thus, Mondays are often seen as a misfortune. In Middle Eastern countries, however, the beginning of the workweek is usually Saturday (Thursday and Friday are observed as the weekend). In Israel, Sunday is the first day of the workweek. Friday is half a work day and Friday night and Saturday are the Sabbath.
This is all from Wikipedia. I can say it in two words only: Mondays suck!