The conventional narrative of Islamic history divides the age of the caliphates into three successive dynasties: the R?shid?n caliphs, the Umayyads, and the ?Abb?sids. Prevalent in both modern and classical scholarship, this categorization is not entirely accurate for it neglects the period of the Second Fitna and the role played by ?Abd All?h b. al-Zubayr b. al-?Aww?m, perhaps the greatest challenger to dynastic succession in his time and any other. Recognized by a significant number of his contemporaries as the legitimate caliph, Ibn al-Zubayr was the key figure in the second Islamic civil war, which ended with his death in 73/692 after his open proclamation of the caliphate for a period of nine years. The early period during which Ibn al-Zubayr lived and pressed his claims for authority was a time of great flux as political, religious, and social conventions were still being formed. Thus, although he is often viewed as the anti-caliph, rebelling against the established Umayyad dynasty, it is arguable that there was no contemporary conception of the Umayyad dynasty as such. Leading members of the Umayyad family exerted every effort to maintain their grip on authority, but nonetheless, at times Ibn al-Zubayr conceivably had a greater claim to the caliphate than his Umayyad rivals because he enjoyed greater support in the Islamic empire. Ibn al-Zubayr’s movement presented a challenge for Islamic historians and scholars from ?abar? and Mas??d? to Dhahab? and ?uy??? and Ibn ?As?kir. It is worth examining the classical Islamic sources, including historical narratives and biographical dictionaries, and analyzing how such scholars, among others, dealt with the question of Ibn al-Zubayr’s legitimacy. What role did factors such as his piety, his family background, his opposition to the Umayyad house, and his control of the holy cities and leadership of the pilgrimage play in determining their views regarding the acceptability of Ibn al-Zubayr’s rule, and how did scholars’ positions evolve over time? Examining their treatment of Ibn al-Zubayr could help us reassess Islamic concepts of communal leadership and spiritual legitimacy, and move us towards a more accurate periodization of the earliest period of Islamic history.