Adherents of Shi‘ism, the second largest denomination of Islam, after Sunnism; those who, in addition to following the sunna of Prophet Muhammad, believe in the Imamat of ʿAlī b. Abī Ṭālib and his descendants through Fatima. The three primary Shi‘i groups are the Ithna‘asharis , the Ismailis and the Zaydis.