A caliphate is the traditional Islamic form of government, presided over by a caliph, either appointed or elected, who is considered the political leader of all Muslims. The caliphate also incorporates a shura, a body similar to a parliament, that represents the will of the people and may elect and/or advise the caliph. Though originally, and ideally according to some, a caliphate — or the caliphate — is a unique entity that unites all Muslims under its rule, there have been concurrent and even competing caliphates at some points in history.

The caliphate began after the death of Mohammed, the first four caliphs being his followers. The institution of the caliphate was intended to carry the legacy of Mohammed's authority. Politically powerful Islamic entities throughout history, including the Ottoman Empire, were incarnations of the caliphate. In 1924, Turkish President Gazi Mustafa Kemal Atatürk abolished the caliphate.

While the majority of caliphates have been centered in the Middle East and exercised authority over Muslims around the world, a notable exception is the Caliphate of Córdoba that ruled the Iberian Peninsula during the 10th and 11th centuries. The Iberian Peninsula became part of the Islamic Empire during the 8th century, when the Ummayad Caliphate ruled out of Damascus. In 750, the Abassids overthrew the Ummayads in the Middle East, marking the beginning of a five-century dynasty. However, descendents of the Ummayads remained in control of Spain, eventually setting up a caliphate there. Many of Spain's most famous and beautiful buildings date from the period of the caliphate, including the Great Mosque of Córdoba.

Though the caliphate in the Middle East was a significant political force in the world into the 20th century, there have been no successful attempts to reinstate it. Several groups, including al-Qaeda, have recently expressed a desire or intention to reestablish the caliphate. However, different groups have widely divergent positions regarding the particulars of how such a caliphate would be established and run, and many who would favor reinstating a caliphate are not political extremists. United States President George W. Bush has spoken vehemently against the restoration of the caliphate, which he claims is a threat to world freedom.