In international standard ISO-8601 the International Organization for Standardization (ISO) has decreed that Monday shall be the first day of the week.

If you define a "week" as a 7-day period, obviously the answer is no. But if you define a "week" as a named interval that is greater than a day and smaller than a month, the answer is yes .The ancient Egyptians used a 10-day "week", as did the French Revolutionary calendar. The Maya calendar uses a 13 and a 20-day "week". The Soviet Union used both a 5-day and a 6-day week. In 1929-30 the USSR gradually introduced a 5-day week. Every worker had one day off every week, but there was no fixed day of rest. On 1 September 1931 this was replaced by a 6-day week with a fixed day of rest, falling on the 6th, 12th, 18th, 24th, and 30th day of each month (1 March was used instead of the 30th day of February, and the last day of months with 31 days was considered an extra working day outside the normal 6-day week cycle). A return to the normal 7-day week was decreed on 26 June 1940. Lithuanians used a week of nine days before adopting Christianity.

The story of Noah contains many allusions to seven days. Note the following in Chapters 7 and 8 of Genesis:

Although some forms of life exhibit cycles of 29-30 days (influenced by the Moon) there is no naturally occurring cycle of seven days. In human society at present this cycle runs on continuously but it has no harmonious relation with the other units of time, the month and the year. The 7-day week exists solely because of social habit and religious tradition, with otherwise no justification. The synodic month (a.k.a. the mean lunar month ) is the mean (that is, average) interval in days between exact conjunctions of the Moon and the Sun (as observed from the Earth). The current value of the synodic month (rounded to six decimal places) is 29.530588 days.

The fixed 7-day week is so much a part of daily life that it is commonly assumed to be as old as human society. It is not known for sure when the system of fixed 7-day weeks, with no relation to the lunar cycle, came into use, but probably lie in Sumerian/Babylonian culture. Some Historians believe that around 2350BC. Sargon I, King of Akkad, having conquered Ur and the other cities of Sumeria, instituted a seven-day week, the first to be recorded. The Jews were commanded to observe "the seventh day" as one on which no work was to be performed (in contrast to the other days when work was done). If this is understood as every seventh day (rather than the seventh day of some period such as the month) then a sequence of fixed 7-day weeks emerges. The fixed 7-day week was not widely used until it was introduced into the Julian Calendar in the 4th Century CE by the Emperor Constantine. Through accidents of history, the Gregorian Calendar has come to be used worldwide as the standard civil calendar for government and business affairs. No improvement has been made in this calendar since it was decreed by Pope Gregory in 1582.

The Need for a Calendar A calendar is necessary to help me, my family, my fellow-workers, and the world's peoples keep track of time. Its purpose is to keep us in touch with appointments and events at home, in the office and world wide.. Currently there are several calendars in use throughout the world. Most are religious calendars used mainly to identify the dates of religious festivals celebrated by the world's many religions. Amongst these is the sacred calendar of the Creator . The sacred calendar is based on the movements of the sun and the moon. It is also linked accurately to many past world events as well as Bible prophecies which describe world-encompassing events shortly to take place. Bible prophecy clearly tells us that there is coming a 'great tribulation, such as was not since the beginning of the world to this time, no, nor ever shall be.' After the tribulation there will be ' signs in the heavens .'