The Fatimid Islamic Caliphate or al-Fāṭimiyyūn (Arabic الفاطميون) was a Shi'a Ismaili Muslim caliphate that spanned a vast area of the Arab World, from the Red Sea in the east to the Atlantic Ocean in the west. Originally based in Tunisia, the Fatimid dynasty extended their rule across the Mediterranean coast of Africa, and ultimately made Egypt the centre of their caliphate. At its height, in addition to Egypt, the caliphate included varying areas of the Maghreb, Sudan, Sicily, the Levant, and Hijaz.

The Fatimids established the Tunisian city of Mahdia and made it their capital city, before conquering Egypt, and building the city of Cairo in 969. Thereafter, Cairo became the capital of the caliphate, with Egypt becoming the political, cultural, and religious centre of the state. The 4th century AH /10th century CE has been called by Louis Massignon ‘the Ismaili century in the history of Islam’.

The term Fatimite is sometimes used to refer to the citizens of this caliphate. The ruling elite of the state belonged to the Ismaili branch of Shi'ism. The leaders of the dynasty were also Shia Ismaili Imams, hence, they had a religious significance to Ismaili Muslims. They are also part of the chain of holders of the office of Caliph, as recognized by some Muslims. Therefore, this constitutes a rare period in history in which the descendants of Ali (hence the name Fatimid, referring to Ali's wife Fatima) and the Caliphate were united to any degree, excepting the final period of the Rashidun Caliphate under Ali himself.