This paper examines what came to be known as the Baghdad Manifesto, the public proclamation sponsored by the Abbasid Caliph al-Qādir in 402/1011 to undermine the legitimacy of the Fatimid claim to the Caliphate by denying their lineal descent from the Prophet Muhammad. The issuance of the document, its ratification by a number of esteemed scholars and leaders of the ashrāf, its pronouncement in mosques across Abbasid lands and its systematic incorporation in Abbasid historiography in the centuries that followed, cumulatively meant that this document subsequently became a standardised proof-text for the illegitimacy of the Fatimid claim. Yet, despite the frequent reference to the proclamation of the Manifesto, a study of the political and social dynamics that led to the issuance of this document, as well as its historiographical trajectory, remains incomplete until now. Through a systematic review of a range of Abbasid as well as Fatimid sources, this paper explores salient issues underpinning Fatimid-Abbasid relations leading to the proclamation of the Manifesto and its aftermath. It also examines the pivotal role of the ashrāf and their enigmatic and shifting alliances with both the Fatimids and the Abbasids in Iraq, Egypt and the Hijaz.