Wikipedia
Ismāʿīlism ( al-Ismāʿīliyya; ; ; ; Esmāʿiliyān) is a branch of Shia Islam. The Ismāʿīlī get their name from their acceptance of Imam Isma'il ibn Jafar as the appointed spiritual successor ( Imām) to Ja'far al-Sadiq, wherein they differ from the Twelvers who accept Musa al-Kadhim, younger brother of Isma'il, as the true Imām.
Tracing its earliest theology to the lifetime of Muhammad, Ismailism rose at one point to become the largest branch of Shī‘ism, climaxing as a political power with the Fatimid Caliphate in the tenth through twelfth centuries. Ismailis believe in the oneness of God, as well as the closing of divine revelation with Muhammad, whom they see as "the final Prophet and Messenger of God to all humanity". The Ismāʿīlī and the Twelvers both accept the same initial Imams from the descendants of Muhammad through his daughter Fatimah and therefore share much of their early history. Both groups see the family of Muhammad (the Ahl al-Bayt) as divinely chosen, infallible ( ismah), and guided by God to lead the Islamic community ( Ummah), a belief that distinguishes them from the majority Sunni branch of Islam.
After the death of Muhammad ibn Isma'il in the 8th century CE, the teachings of Ismailism further transformed into the belief system as it is known today, with an explicit concentration on the deeper, esoteric meaning ( batin) of the Islamic religion. With the eventual development of Twelverism into the more literalistic ( zahir) oriented Akhbari and later Usuli schools of thought, Shi'i Islam developed into two separate directions: the metaphorical Ismaili group focusing on the mystical path and nature of God, with the "Imām of the Time" representing the manifestation of esoteric truth and intelligible reality, with the more literalistic Twelver group focusing on divine law ( sharia) and the deeds and sayings ( sunnah) of Muhammad and the Twelve Imams who were guides and a light to God. Ismaili thought is heavily influenced by neoplatonism.
Though there are several paths ( tariqat) within Ismailism, the term in today's vernacular generally refers to the Nizaris, who recognize the Aga Khan IV as the 49th hereditary Imam and is the largest Ismaili group. In recent centuries Ismāʿīlīs have largely been a Pakistani, Afghan, and Indian community, but Ismailis are also found in Bangladesh, Syria, Iran, Saudi Arabia, Yemen, Jordan, Kurdistan, East Africa, Angola, Lebanon, and South Africa, and have in recent years emigrated to Europe, Canada, Australia, New Zealand, the United States, and Trinidad and Tobago. There are also a significant number of Ismāʿīlīs in Central Asia.