A caliphate or khilāfah (خِلَافَة, xi'laːfah) is an institution or public office under the leadership of an Islamic steward with the title of caliph (ˈkælɪf,_ˈkeɪ-; خَلِيفَة xæ'liː'fæh, ), a person considered a political-religious successor to the Islamic prophet Muhammad and a leader of the entire Muslim world (ummah). Historically, the caliphates were polities based on Islam which developed into multi-ethnic trans-national empires. During the medieval period, three major caliphates succeeded each other: the Rashidun Caliphate (632–661), the Umayyad Caliphate (661–750), and the Abbasid Caliphate (750–1258). In the fourth major caliphate, the Ottoman Caliphate, the rulers of the Ottoman Empire claimed caliphal authority from 1517 until the caliphate was abolished as part of the 1924 secularisation of Turkey. Throughout the history of Islam, a few other Muslim states, almost all hereditary monarchies such as the Mamluk Sultanate (Cairo) and Ayyubid Caliphate, have claimed to be caliphates.
Not all Muslim states have had caliphates. The Sunni branch of Islam stipulates that, as a head of state, a caliph should be elected by Muslims or their representatives. Shiites, however, believe a caliph should be an imam chosen by God from the Ahl al-Bayt (the "Household of the Prophet").
In the early twenty-first century, following the failure of the Arab Spring and related protests, some have argued for a return to the concept of a caliphate to better unify Muslims.
Before the advent of Islam, Arabian monarchs traditionally used the title malik (King, ruler), or another from the same root.
The term caliph (ˈkeɪlɪf,_ˈkælɪf), derives from the Arabic word ALA (خَليفة, ), which means "successor", "steward", or "deputy" and has traditionally been considered a shortening of Khalīfat Rasūl Allāh ("successor of the messenger of God"). However, studies of pre-Islamic texts suggest that the original meaning of the phrase was "successor selected by God".