Abstrak
Mankinds needs a calendar as a regulator and time divider. Especially for Muslims, the need for a calendar is very urgent because there are many Muslim worships related to time, such as the Hajj, Ramadan fasting and other purposes. There are two systems of calendars based on the circulation times of heavenly bodies. First, the Christian calendar is a dating system based on the average circulation of the Earth around the Sun (Solar System). Second, the Hijri Calendar is a calendar based on the average circulation of the moon around the Earth (Lunar System). The criteria clearly affect the uncertainty of the Islamic Calendar. Then it is necessary to unite the Islamic calendar universally. One of the initiators in uniting the Islamic calendar is Jamaluddin Abdur Raziq which is contained in at-Taqwim al-Qamariy al-Islam al-Muwaahid or famous for the term Universal Islamic Calendar. This idea arises because of the differences that often occur in beginning and ending the beginning of the lunar month. In this concept Jamaluddin Abdur Raziq hopes that all Muslims throughout the world have a permanent Islamic calendar. The method applied in this paper is descriptive analysis. The author will describe the concept of Jamaludin Abdur Raziq's idea of the unification of the Islamic Calendar. After describing it, then it will analyze the implementation of the idea of Jamaludin Abdur Raziq in Indonesia.