The Shia (Arabic: شيعة Shīʿah) represent the second largest denomination of Islam and adherents of Shia Islam are called Shias or the Shi’a as a collective or Shi’i individually. Shi’a is the short form of the historic phrase Shīʻatu ʻAlī (شيعة علي) meaning “followers”, “faction” or “party” of Muhammad’s son-in-law and cousin Ali, whom the Shia believe to be Muhammad’s successor in the Caliphate. Twelver Shia (Ithnā’ashariyyah) is the largest branch of Shia Islam and the term Shia Muslim is often taken to refer to Twelvers by default. Shia Muslims constitute 10-20% of the world’s Muslim population and 38% of the Middle East’s entire population.
Shi’i Islam is based on the Quran and the message of the Islamic prophet Muhammad attested in hadith recorded by the Shia, and certain books deemed sacred to the Shia (Nahj al-Balagha). In contrast to other Muslims, the Shia believe that only God has the right to choose a representative to safeguard Islam, the Quran and sharia. Thus the Shia look to Ali, Muhammad’s son-in-law, whom they revere and consider divinely appointed, as the rightful successor to Muhammad, and the first Imam. In the centuries after the death of Muhammad, the Shia extended this “Imami” doctrine to Muhammad’s family, the Ahl al-Bayt (“the People of the House”), and certain individuals among his descendants, known as Imams, who they believe possess special spiritual and political authority over the community, infallibility, and other quasi-divine traits.
Although there are myriad Shi’i subsects, modern Shi’i Islam has been divided into three main groupings: Twelvers, Ismailis and Zaidis.