From the beginning of the Islamic history, the scholars developed the Islamic hijri calendar as a lunar calendar designed to organize timekeeping for religious and social needs. The development of the Islamic calendar and the different tasks related to it played a leading role in the advance of Arabic astronomy as an applied and theoretical science. The following article presents a survey on the Islamic hijri calendar and the varieties of timekeeping devices related to it. A special concern is devoted to the Ottoman contributions in this field.
