Imamah is the Shia Islam doctrine (belief) of religious, spiritual and political leadership of the Ummah. The Shia believe that the Imams are the true Caliphs or rightful successors of Muhammad, and further that Imams are possessed of divine knowledge and authority (Ismah) as well as being part of the Ahl al-Bayt, the family of Muhammad. These Imams have the role of providing commentary and interpretation of the Quran as well as guidance to their tariqa followers as is the case of the living Imams of the Nizari Ismaili tariqah.