member of the smaller of the two major branches of Islam, distinguished from the majority Sunnis (Sunnite).

Early in the history of Islam, the Shīʿites were a political faction (Arabic shīʿat ʿAlī, “party of ʿAlī”) that supported the power of ʿAlī ibn Abī Ṭālib (Alīʿ) (the fourth caliph 【khalīfah, successor of Muhammad】) and, later, of his descendants. Starting as a political faction, this group gradually developed into a religious movement, Shīʿism, which not only influenced Sunni Islam but also produced a number of important sects to which the term Shīʿah is applied.

The Prophet Muhammad died in AD 632 without an heir, none of his sons having survived to adulthood, and a broad consensus of those present at Medina nominated his longtime companion Abū Bakr as his successor. Abū Bakr died two years later and was succeeded in the caliphate by his assistant and adviser ʿUmar ibn al-Khaṭṭab (Umar Iʿ). When ʿUmar was assassinated by a disgruntled Persian slave in 644, Uthmān ibn ʿAffānʿ was selected by a committee to become the third caliph. ʿUthmān was killed by rebels in 656.

From the time of the first caliph, a number of those within the Muslim community felt that ʿAlī ibn Abī Ṭālib, who was Muhammad's first cousin and close confidant as well as his son-in-law and the father of Muhammad's grandsons Ḥasan and al-Ḥusayn (Ḥusayn ibn ʿAlī, al-) (by Muhammad's daughter Fāṭimah), was the natural choice to succeed the Prophet. In 656 ʿAlī was raised to the caliphate, partly with the support of those who had murdered the third caliph, ʿUthmān.

ʿAlī never quite received the allegiance of all the Muslims, however, and, in an effort to consolidate power, he was forced to wage a series of campaigns in an insurrection that came to be known as the first fitnah (“trial”). ʿAlī's main opponent was the Muslim governor of Syria, Muʿāwiyah ibn Abī Sufyān (Muʿāwiyah I), who was a kinsman of the murdered ʿUthmān (both men were members of the Umayyad clan—founders of the Umayyad Dynasty—whose leaders had been fierce adversaries of Muhammad before their conversion to Islam). The antagonism between ʿAlī and Muʿāwiyah culminated in the Battle of Ṣiffīn (Ṣiffīn, Battle of) (657), a conflict that ʿAlī appeared to be winning until he agreed to Muʿāwiyah's demand for arbitration. ʿAlī's concession angered a large faction within his forces, and the malcontents soon seceded (and were henceforth known as the Khārijites, “Seceders”), which ultimately weakened ʿAlī's position. ʿAlī was murdered by a Khārijite in 661.

Swearing vengeance against the triumphant Umayyad government, the remorseful residents of Al-Kūfah soon engaged in a series of unsuccessful insurrections against Umayyad rule. These were put down with great brutality, notably by the Umayyad provincial governor al-Ḥajjāj (Ḥajjāj, al-). In one such insurrection, the Shīʿite leader al-Mukhtār ibn Abī ʿUbayd al-Thaqafī (Mukhtār ibn Abū ʿUbayd al-Thaqafi, al-) put forward Muḥammad ibn al-Ḥanafiyyah (Muḥammad ibn al-Ḥanafīyah), a son of ʿAlī from a wife other than Fāṭimah, as caliph. Such revolts tended to have a strong millenarian element, and, in the turbulent social and political circumstances of the late 7th and early 8th centuries, political differences slowly began to take on theological proportions. Extremist (ghulāt) groups began to proliferate, often attributing miraculous, even divine, status to ʿAlī and his family.

The people of Al-Kūfah ultimately gained support from other groups that opposed the status quo of the Umayyad dynasty. These included aristocratic Muslim families of Medina, pious men protesting what they considered too worldly an interpretation of Islam, and non-Arab Muslims (mawālī, “clients”), especially in Iraq, who demanded an equality denied them by the ruling Arabs.

The subsequent revolt, which ended in 750, finally put an end to Umayyad power; however, rather than an ʿAlid rising to the caliphate, the appointment went to a scion of another branch of the Prophet's family, one descended from Muhammad's uncle al-ʿAbbās. Under the Abbāsid Dynastyʿ (750–1258), the theological, philosophical, and legal superstructure of what was to become the Sunni community developed and flourished. The insurrections of the Umayyad period died down, but a counterculture developed in the form of several diverse groups promoting Shīʿite candidates to leadership. One such group, the Zaydiyyah (Zaydīyah) (named for Zayd ibn ʿAlī, a grandson of al-Ḥusayn), formulated its principles in the 9th century. The Zaydīs (members of the Zaydiyyah) demanded, sometimes with sword in hand, that the ruler be whichever descendant of Ḥasan or al-Ḥusayn (that is, the sons of ʿAlī by Fāṭimah) was proved qualified, at a given time, by his religious knowledge and his practical ability. Zaydī devotees set up several small states along the Caspian littoral in what is now northern Iran and in Yemen in southern Arabia, where Zaydī imams have since been spiritual leaders and where they ruled politically until 1962.

Zaydīs differed only marginally from mainstream Sunnis in their views on political leadership, but it is possible in this sect to see a refinement of Shīʿite doctrine. Early Sunnis traditionally held that the political leader must come from the tribe of the Prophet—namely, the Quraysh. The Zaydīs narrowed the political claims of the ʿAlids, claiming that not just any descendant of ʿAlī would be eligible to lead the Muslim community (ummah) but only those males directly descended from Muḥammad through the union of ʿAlī and Fāṭimah (the sect of Muhammad ibn al-Ḥanafiyyah died out in the 9th century).

Other Shīʿites, who came to be known as imāmiyyah (followers of the imams 【religious leaders】), narrowed the pool of potential leaders even further and asserted a more exalted religious role for the ʿAlid claimants. They insisted that, at any given time, whether in power or not, a single male descendant of ʿAlī and Fāṭimah was the divinely appointed imam and the sole authority, in his time, on all matters of faith and law. The more speculative among them, the ghulāt, sometimes bestowed practically divine honours on the imams. The more moderate came, in time, to claim that at least a supernatural “Muhammadan light” embodied in the imams gave them superhuman knowledge and power and that their sufferings were a means of divine grace to their devotees. To those Shīʿites, love of the imams and of their persecuted cause became as important as belief in God's oneness and the mission of Muhammad. Under Sunni rule, the imāmiyyah often were violently persecuted and sometimes protected themselves by dissimulating their faith (taqiyyah (taqiya)), but Shīʿite doctrine eventually came to hold that the imam, as mahdi (mahdī) (a divine saviour), would deliver the faithful and punish their enemies.

Most Shīʿites eventually came to acknowledge one of two family lines (the imamate passing from father to son) stemming from ʿAlī but diverging at al-Ḥusayn's great-grandson Jaʿfar ibn Muhammad (Jaʿfar ibn Muḥammad) (also called Jaʿfar al-Ṣādiq). After Jaʿfar's death (765), one group opted to follow his son Ismāʿīl. They became known as the Ismāʿīliyyah (Ismāʿīlīte) or the Seveners, because Ismāʿīl was the seventh and final imam in their lineage. The Ismāʿīlīs developed a unique religious system and established a caliphate of their own, ruled by the Fāṭimid Dynasty (909–1171), in North Africa, which later spread to Egypt and briefly took power in the Levant. Ismāʿīlī devotees (notably the Assassins (Assassin)) also proselytized in Iraq, Iran, and other parts of the Mashriq (the region between the western border of Egypt and the western border of Iran).

This brand of Shīʿism was extremely esoteric and never developed a mass following in its realms. Most Fāṭimid subjects remained Sunni, but the sect survived in the offshoot Druze faith of Lebanon and Syria and in the present-day Khoja (Khōjā) and Bohra (Bohrā) merchant communities of India and easternAfrica. The Khojas, who are descended from the Nizārī branch of the Ismāʿīlīs, continue to follow the aga khans, a lineage of Muslim spiritual leaders who claim direct descent from ʿAlī. Another Ismāʿīlī dynasty, the Qarmatians (Qarmatian), was active in eastern Arabia from the 9th through the 11th century.

Most Shīʿites now acknowledge another line, one descended from a second son of Jaʿfar, Mūsā al-Kāẓim. This lineage ended with the Twelfth Imam, Muḥammad al-Mahdī al-Ḥujjah, when he purportedly went into occultation ( ghaybah) in 878. Consequently, this branch of Shīʿism is referred to as the Ithnā ʿAshariyyah (Ithnā ʿAsharīyah) (“Twelvers”). As his name might suggest, the Twelfth Imam, or Hidden Imam, as he is often known, took on eschatological significance for the followers of this branch of Shīʿism. He is expected to return as the mahdi before the Last Judgement to establish justice on earth.

Other groups associated with the Ithnā ʿAshariyyah are the ʿAlawites (Alawiteʿ) (Nuṣayriyyah) of Syria (the dominant political group in Syria in the late 20th and early 21st centuries); the ʿAlī Ilāhīs or Ahl-e Haqq (Ahl-e Ḥaqq), who are mostly scattered herdsmen and farmers of Kurdistan, Turkey, and Iran; and the Bektāshī (Bektashi) order of dervishes (dervish) in Turkey and Albania.

In addition to the Ismāʿīlī dynasties mentioned above, several other Shīʿite dynasties played important roles in Islamic history. The emirs of the Shīʿite Ḥamdānid Dynasty (905–1004) were notable patrons of the arts. One of their renowned leaders, Sayf al-Dawlah (916–967), who fought a long series of campaigns against the Byzantine Empire, was a patron of the great Arab poet al-Mutanabbī, among others. Overlapping the Ḥamdānids chronologically, the Būyid Dynasty (945–1055) dominated much of Iraq and western Iran, occupied Baghdad, and for many years effectively controlled the ʿAbbāsid caliphate. Such was the scope of Shīʿite political power during the 10th century that often it has been referred to as the Shīʿite Century.

By the time of the Ṣafavids, Shīʿite theological and legal doctrine had expanded and matured, precipitating doctrinal disputes that often became vitriolic between factions within the Ithnā ʿAsharī religious community. One faction, known as the Akhbāriyyah, felt that the only sound source of legal interpretation was the direct teachings of the 12 infallible imams, in the form of their written and oral testaments (akhbār). Their opponents, known as the Uṣūliyyah, held that a number of fundamental sources (uṣūl) should be consulted but that the final source for legal conclusions rested in the reasoned judgment of a qualified scholar, a mujtahid (i.e., one who is empowered to interpret legal issues not explicitly addressed in the Qurʾān; see ijtihād). The eventual victory of the Uṣūliyyah in this debate during the turbulent years at the end of the Ṣafavid empire (early 18th century) was to have resounding effects on both the shape of Shīʿism and the course of Islamic history. The study of legal theory ( fiqh; the purview of the mujtahids) became the primary field of scholarship in the Shīʿite world, and the concomitant rise of the mujtahids as a distinctive body signaled the development of a politically conscious and influential religious class not previously seen in the Muslim world.

Over time, Shīʿites became a distinct collection of sects, alike in their recognition of ʿAlī and his descendants as the legitimate leaders of the Muslim community. Although the Shīʿites' conviction that the ʿAlids should be the leaders of the Islamic world was never fulfilled, ʿAlī himself was rehabilitated as a major hero of Sunni Islam, and his descendants by Fāṭimah—who is venerated among Sunnis and Shīʿites alike—received the courtesy titles of sayyids and sharifs.

Shīʿites have come to account for roughly one-tenth of the Muslim population worldwide. The largest Shīʿite sect in the early 21st century was the Ithnā ʿAshariyyah (Ithnā ʿAsharīyah), which formed a majority in Iran, Iraq, Azerbaijan, and Bahrain. The sect also constituted a significant minority in eastern Saudi Arabia and the other Arab states of the Persian Gulf region, as well as in parts of Syria, South Asia, and eastern Africa. The Ithnā ʿAshariyyah was the largest Shīʿite group in Lebanon, and Shīʿites in that country, as well as in Iran and Iraq, were among the most vocal representatives of militant Islamism. Smaller Shīʿite sects included the Ismāʿīliyyah (Ismāʿīlīte), who formed the bulk of the Shīʿite community in parts of Pakistan, India, and eastern Africa, and the Zaydiyyah (Zaydīyah), who lived almost exclusively in northwestern Yemen. Various subsects of Shīʿism were also found in other parts of the Muslim world.