For most observant Christians, Sunday is observed as a day of worship and rest, holding it as the Lord's Day and the day of Christ's resurrection. In some Muslim countries and Israel, Sunday is the first work day of the week. According to the Hebrew calendar and traditional Christian calendars, Sunday is the first day of the week. But according to the International Organization for Standardization ISO 8601, Sunday is the seventh day of the week.

What's the best answer to this question: what day is the first day of the week?
no