The Nizaris are the largest segment of the Ismaili Muslims, who are the second-largest branch of Shia Islam after the Twelvers. Nizari teachings emphasize independent reasoning or ijtihad; pluralism—the acceptance of racial, ethnic, cultural and inter-religious differences; and social justice. Nizaris, along with Twelvers, adhere to the Jaʽfari school of jurisprudence. The Aga Khan, currently Aga Khan IV, is the spiritual leader and Imam of the Nizaris. The global seat of the Ismaili Imamate is in Lisbon, Portugal.

Isma'ilism is a branch or sect of Shia Islam. The Isma'ili 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 Twelver Shia, who accept Musa al-Kadhim, the younger brother of Isma'il, as the true Imām.