Shia Islam is the second-largest branch of Islam. It is rooted in the belief that the Islamic prophet Muhammad explicitly designated his cousin and son-in-law Ali ibn Abi Talib () as his rightful political successor (caliph) and the divinely guided spiritual leader of the Muslim community (imam). Shia Muslims maintain that Ali's divine right to leadership was unjustly usurped at the meeting of Saqifa, where certain companions of Muhammad apparently acted against the Prophet's mandate to appoint Abu Bakr () as caliph. While Sunni Muslims accept the rule of Abu Bakr, Umar (), and Uthman (), Shia Muslims remain steadfast in honouring what they perceive to be the Prophet's wishes, recognizing Ali alone as Muhammad's true and legitimate successor.
Shia Muslims believe the imamate continued rightfully through Ali's sons, Hasan and Husayn, after whom various Shia branches emerged to follow the lines of the true imams. Central to Shia devotion is a profound reverence for the , the purified family of Muhammad, who are recognized as the infallible inheritors of his divinely granted knowledge and spiritual authority. Sacred Shia holy sites include the shrine of Ali in Najaf, the shrine of Husayn in Karbala, and other mausoleums of the revered .
Shia Muslims constitute an estimated 10–13%See
of the world's Muslim population, numbering approximately 200–260 million faithful followers as of 2026. The three principal Shia branches are Twelverism, Isma'ilism, and Zaydism. Shia Muslims form a majority in Iran, Iraq, and Azerbaijan while making up almost half of the Muslim population of Lebanon and Bahrain. Substantial Shia communities also exist in Turkey, Yemen, Saudi Arabia, Afghanistan, and the Indian subcontinent. Iran remains the only country in the world where Shia Islam officially serves as the foundation of both its legal framework and system of governance.
Etymology The word Shia (or ; ; ) is derived from ().The New Encyclopædia Britannica, 15th ed., Encyclopædia Britannica, Inc., 1998, , Vol. 10, p. 738 An adherent is called a Shi'i (; ; ). In Arabic, "Shīʿa" means followers and supporters; the term derives from al-shiyāʿ and al-mushāyaʿa, which convey the meanings of following, supporting, and obedience. Shia Islam is also referred to in English as Shiism (or Shīʿism) (), and Shia Muslims as Shiites (or Shīʿites) ().
The term was first used during Muhammad's lifetime. At present, the word refers to Muslims who believe that the leadership of the Muslim community after Muhammad belongs to ʿAlī ibn Abī Ṭālib, Muhammad's cousin and son-in-law, and his successors.
Nawbakhti states that the term Shia refers to a group of Muslims who, at the time of Muhammad and after him, regarded ʿAlī as the Imam and caliph. Al-Shahrastani explains that the term Shia refers to those who believe that ʿAlī was designated as the heir, Imam, and caliph by Muhammad, and that ʿAlī's authority is maintained through his descendants. For the adherents of Shia Islam, this conviction is implicit in the Quran and the history of Islam. Shia Muslim scholars emphasize that the notion of authority is linked to the family of the Abrahamic prophets, as the Quranic verses and illustrate: "Indeed, Allah chose Adam, Noah, the family of Abraham, and the family of 'Imrân above all people. They are descendants of one another. And Allah is All-Hearing, All-Knowing."
History
The original Shia identity referred to the followers of Imam ʿAlī,"Shiʻite Islam", by Allamah Sayyid Muhammad Husayn Tabataba'i, translated by Sayyid Husayn Nasr, State University of New York Press, 1975, p. 24 and Shia theology was formulated after the hijra (7th century CE).Dakake (2008), pp. 1–2 The first Shia governments and societies were established by the end of the 9th century. The 10th century has been referred to by the scholar of Islamic studies Louis Massignon as "the Shiite Ismaili century in the history of Islam".In his "Mutanabbi devant le siècle ismaëlien de l'Islam", in Mém. de l'Inst Français de Damas, 1935, p.
Origins
The Shia, originally known as the "partisans" of ʿAlī ibn Abī Ṭālib, Muhammad's cousin and Fatima's husband, first emerged as a distinct movement composed of those fiercely loyal to him during the First Fitna (656–661). Shia doctrine is founded on the understanding that ʿAlī was uniquely designated to lead the Muslim community after Muhammad's death in 632. While the origins of Shia Islam remain a subject of scholarly debate, many Western historians have attempted to characterize early Shia Islam merely as a political faction rather than a religious movement,See: Lapidus p. 47, Holt p. 72Francis Robinson, Atlas of the Islamic World, p. 23. while others recognize this framework as an anachronistic imposition of the Western separation of religion and politics.Jafri, S.H. Mohammad. "The Origin and Early Development of Shiʻa Islam", Oxford University Press, 2002, p. 6,
Shia Muslims point to Muhammad's explicit designation of ʿAlī as his successor during a major sermon at Ghadir Khumm, in which he declared: "Anyone who has me as his , has ʿAlī as his ".Esposito, John. "What Everyone Needs to Know about Islam". Oxford University Press, 2002 | . p. 40 Many versions of the sermon include the invocation: "O God, befriend the friend of ʿAlī and be the enemy of his enemy". The interpretation of this prominent proclamation is central to the Sunni–Shia divide: while Sunni scholars tend to interpret it as a general affirmation of ʿAlī's merit, Shia Muslims maintain it to be a clear and unambiguous designation of ʿAlī as Muhammad's appointed successor. Shia sources further record that those present at Ghadir Khumm immediately congratulated ʿAlī, acclaiming him as ("commander of the believers").
When Muhammad died in 632 CE, ʿAlī and Muhammad's closest relatives remained occupied with the solemn duty of his funeral arrangements. While they were preparing his body, Abū Bakr, ʿUmar ibn al-Khaṭṭāb, and Abu Ubaidah ibn al Jarrah convened a separate meeting with the leaders of Medina at Saqifa and secured the election of Abū Bakr as the first of the rāshidūn caliphs. While Sunni Muslims maintain that this election was politically legitimate, the process had no clear basis or precedent set by Muhammad, and ʿAlī's partisans viewed it as a direct violation of the Prophet's designation at Ghadir Khumm. Abū Bakr served from 632 to 634, followed by ʿUmar (634–644) and ʿUthmān (644–656).
Following the assassination of ʿUthmān in 656, the Muslims of Medina finally turned to ʿAlī as the fourth caliph, and he established his capital in Kufa. ʿAlī's subsequent rule over the early Islamic empire (656–661) was marked by entrenched opposition from rival factions. The resulting conflict, known as the First Fitna, became the first major civil war within the Muslim community, encompassing a series of revolts against ʿAlī by groups that had initially affirmed the legitimacy of his caliphate before ultimately turning against him.
The conflict began with the Battle of the Camel in 656, in which ʿAlī's forces successfully prevailed against the coalition of Aisha, Ṭalḥah, and al-Zubayr. At the Battle of Siffin in 657, ʿAlī's campaign to subdue Muʿāwiyah, the governor of Damascus, was frustrated by a forced arbitration that proved structurally disadvantageous to ʿAlī. He subsequently withdrew to Kufa, where he decisively defeated the Khārijīs — former supporters who had fractured his coalition — at the Battle of Nahrawan in 658. In 661, ʿAlī was assassinated by a Khārijī while in a vulnerable state of prostration during prayer () at the Great Mosque of Kufa. Following this, Muʿāwiyah consolidated power, seized the caliphate, and founded the Umayyad dynasty.The New Encyclopædia Britannica, 15th ed., Encyclopædia Britannica, Inc., 1998, , Vol. 10, p. tid738
Hasan, Husayn, and Karbala
Upon the death of ʿAlī, his elder son Ḥasan assumed leadership of the Muslims of Kufa. After a series of skirmishes between the Kufa Muslims and the army of Muawiyah, Ḥasan ibn ʿAlī agreed to cede the caliphate to Muawiyah and maintain peace among Muslims upon certain conditions: the enforced public cursing of ʿAlī, including during prayers, should be abandoned; Muawiyah should not use tax money for his own private needs; there should be peace, and followers of Ḥasan should be given security and their rights; Muawiyah would never adopt the title of Amir al-Mu'minin ("commander of the believers"); and Muawiyah would not nominate any successor. Ḥasan then retired to Medina, where in 670 CE he was poisoned by his wife Ja'da bint al-Ash'ath, after being secretly contacted by Muawiyah, who wished to pass the caliphate to his own son Yazid and viewed Ḥasan as an obstacle.
Ḥusayn ibn ʿAlī, ʿAlī's younger son and brother to Ḥasan, initially resisted calls to lead the Muslims against Muawiyah and reclaim the caliphate. In 680, Muawiyah died and passed the caliphate to his son Yazid, thereby breaking the treaty with Ḥasan ibn ʿAlī. Yazid demanded that Husayn swear allegiance (bay'ah) to him. ʿAlī's faction, having expected the caliphate to return to ʿAlī's line upon Muawiyah's death, viewed this as a betrayal of the peace treaty, and Ḥusayn refused this demand for allegiance. There was a groundswell of support in Kufa for Ḥusayn to return there and take his position as caliph and Imam, so Ḥusayn gathered his family and followers in Medina and set off for Kufa.
En route to Kufa, Husayn was intercepted by an army of Yazid's men, which included forces from Kufa, near Karbala. Rather than surrendering, Husayn and his followers chose to stand and fight. In the Battle of Karbala, Ḥusayn and approximately 72 of his family members and followers were killed, and Husayn's head was delivered to Yazid in Damascus. The Shia community regards Ḥusayn ibn ʿAlī as a martyr (shahid) and counts him as an Imam from the . The Battle of Karbala and the martyrdom of Ḥusayn ibn ʿAlī are widely cited as the definitive moment of separation between the Shia and Sunnī sects of Islam. Ḥusayn is the last Imam following ʿAlī mutually recognized by all branches of Shia Islam.Discovering Islam: making sense of Muslim history and society (2002) Akbar S. Ahmed The martyrdom of Husayn and his followers is commemorated on the Day of Ashura, occurring on the tenth day of Muharram, the first month of the Islamic calendar.
Imamate of the Ahl al-Bayt
Later, most denominations of Shia Islam, including Twelvers and Ismāʿīlīs, became Imamis. Shia Muslims believe that Imams are the spiritual and political successors to Muhammad. Imams are human individuals who not only rule over the Muslim community with justice but are also able to keep and interpret the divine law and its esoteric meaning. The words and deeds of Muhammad and the Imams serve as a guide and model for the community to follow; as a result, they must be free from error and sin, and must be chosen by divine decree () through Muhammad.Nasr (1979), p. 10 According to this view, which is distinctive to Shia Islam, there is always an Imam of the Age, who is the divinely appointed authority on all matters of faith and law in the Muslim community. ʿAlī was the first Imam of this line, the rightful successor to Muhammad, followed by male descendants of Muhammad through his daughter Fatimah.
This difference between following the Ahl al-Bayt (Muhammad's family and descendants) or pledging allegiance to Abū Bakr has shaped the Shia–Sunnī divide on the interpretation of some Quranic verses, hadith literature (accounts of the sayings and living habits attributed to the Islamic prophet Muhammad during his lifetime), and other areas of Islamic belief throughout the history of Islam. For instance, the hadith collections venerated by Shia Muslims are centred on narrations by members of the Ahl al-Bayt and their supporters, while some hadith transmitted by narrators not belonging to or supporting the Ahl al-Bayt are excluded.