Imam (Arabic, “leader” or “exemplar”), in general usage in Islam, the political head of the Muslim community or the person who leads prayer services. The Prophet Muhammad and his early successors—including those of the Umayyad caliphate—performed both functions; the head of state himself led Friday prayers in the central capital mosque, and his governors did the same in provincial capitals. Later, however, administrative and political functions were separated from religious ones.

In Shia Islam, the term imam is applied to the person who is both the political and religious leader. He must be descended from Ali and Fatima (the son-in-law and daughter of the Prophet Muhammad). No imam, however, except Ali, ever ruled, and beginning with the sixth imam, Jafar al-Sadiq, all eschewed political power. The imam is regarded by the main body of Shia Muslims as immune from error and sin and by the Ismailis as a veritable incarnation of God. Both sects believe the last imam to be in concealment and await his return.