On the death of Muhammad, the question of his succession stemmed between two legitimacies: on the one hand, the Companions backed up by a tribal tradition – the choice of the leader by a council of notables; on the other hand, the "Party of ‘Alī". The Companions were chosen, and ‘Alī became the caliph much later, from 656 to 661. In the Shiite doctrine, according to a hadīth, "People in my family are like Noah's ark. Whoever takes a seat on this arch will be saved. Whoever moves away perishes.” God entrusted the leadership of Muslims to an Imām from the family of the Prophet: ‘Alī, his sons Hasan and Huseyn, and their descendants.
God chose the Imām to unveil the hidden meaning (bātin) of the revelation. Without him, the Quran would remain a "silent Book." The Imām - also called the "speaking Quran" - is the infallible "Guide" of the community. He must be just, "very pure” and the most perfect of all (afzal). According to the Twelver, the Twelfth Imām is living hidden since his “main occultation” in 940, and will return at the end of time to restore justice. In the meantime, he guides believers through scholars, the mullahs. The Twelver legal, mystical and philosophical doctrine was developed during the Abbasid period. It had few differences with the Sunni jurisprudence, except for three subjects: temporary marriage, divorce, and rules of inheritance and succession.
Ismā’īlism and Zaydīsm differ from the Twelver Imamite Shi'a because the genealogy of Imāms was ended before the 12th century, with seven Imāms for the Ismā’īlites and five Imāms for the Zaydis.

Some rites and celebrations are unique to Shi'a. The five prayers are grouped in three stages. The faithful put a small clay pad on the prayer rug and place their forehead on the pad during ritual prostrations. Shi'a in all major areas of the Muslim world have celebrated the mourning of Āshūrā' in various ways (songs, laments, blood, etc.) depending on ethnicities and countries. This does not always include chest beating.
In Pakistan, since the Islamic Revolution of Iran in 1979, deadly “sectarian” violence has regularly opposed Sunnis and Shi'a (about one fifth of the population). The conflict was politicized, and the commemoration of the "martyrdom" of Imām Huseyn has been placed under close police surveillance. In Iran, the tragedy of the "martyrdom" of Huseyn and his family has been traditionally represented by a particular genre called ta'zīya.
The Shi'a worship the tombs of the Imāms and their descendants, considered as descendants of the family of the Prophet. The main devotion centres - the "Holy Thresholds" – are the shrines of the Imāms Huseyn (in Karbala) and ‘Alī (in Najaf) in Iraq and the shrine of Rezā, the Eighth Imām, in Mashhad (Iran).

The history of Shi'a includes several periods. Firstly, the faithful of the "Party of ‘Alī" and the Imāms (until the 10th century) were followed by the setting up of a corpus of traditions and a doctrine from the 10th century to the 13th century. Secondly, between the Mongol invasion and the Safavids of Iran, Shiism became a state doctrine with numerous works in literature, philosophy, theology, mysticism, etc. Thirdly, from the 16th century to the present, the religion was instrumentalized into politics with the doctrine of velāyat-e-faqīh.
The theory of the "sovereignty of the legal theologian" has not been shared unanimously by all the main religious figures of Shiism in Iran, Lebanon, Afghanistan and Iraq. In 1989, the choice of a successor to Khomeini – “Leader of the Revolution” - fell on Khamenei, a little-known ayatollah, who was given the political role of Guide of the Islamic Republic.