Imamite Shias form the largest branch of the Shia sect and their identity lies in the recognition of the Twelve Imams. For this reason they are also known as the Twelvers. They believe in twelve divinely ordained leaders known as Imams. The Mahdi, for them, is none other than the twelfth Imam who had disappeared and was believed to be in occultation. Most of the teachings and tenets of Shiaism are held in common by the Twelvers. However, certain groups, such as, the Ismaili and Zaydi sects, have certain differing notions on the number of Imams, the definition of Imam etc. The end of the ninth century is the period in which Imamite Shiaism took definite shape.

The chief doctrine of the Imamites is that Ali had been clearly designated Imam or leader of the community by the Prophet Muhammad in succession to himself, and was therefore the rightful leader of the Muslim faith. This implied that such designation by the preceding Imam was the proper title to succession. Each Imam was the son of the previous Imam, with the exception of Husayn Ibn Ali, who was the brother of Hasan Ibn Ali. The twelfth and final Imam is Muhammad al Mahdi, who is believed by the Twelvers to be currently alive, and in hiding. The descendants of the Prophet through his son in law Ali were held to be the best authority in the interpretation of the Holy Quran and the Sunna. The Imamites do not recognize the leadership of the first three Caliphs, Abu Bakr, Uthman and Umar. For them the first Imam was Ali himself and he was appointed by God, unlike in the case of the Sunnis whose leaders were democratically elected. They do not accept the verdicts and Ahadiths of the first three Caliphs. They also contribute the concept of infallibility to the twelve Imams.

The Imamite Shias also believe in the five pillars of Islam, much like the Sunnis, even though there categorization was different. The principles of Faith for the Imamite Shias include- Tawhid belief in the oneness of God, Ada or the justice of God, Nubuwwah or Prophethood, Imamah or leadership and Qiyamah or the day of judgement. The branches of religions for the Imamite Shias include Salat, Sawm, Zakat, Khums, Hajj, Twalla and Tabarra.

The Twelve Imamas were at the centre stage of Imamite Shiasm. They were held to be the spiritual and political successors to Muhammad. He is believed to be an infallible human individual who ruled over the community with justice and is able to keep and interpret the Sharia and its esoteric meaning. The words and deeds of the Prophet and the Imamas are to act as a guide for the community in their actions. The esoteric knowledge or Hikmah was obtained by the Prophets and Imams by means of `Aql`, a divine wisdom which was the source of the souls of the prophets.