The Tathbīt al-imāma attributed to the Fatimid Caliph-Imam al-Manṣūr (334–341/946–953) is an important early Ismaili treatise on the legitimacy of the imamate of ʿAlī b. Abī Ṭālib and that of the Ismaili imams from among his progeny.

As one of the earliest Ismaili works on this crucial and fundamental Shiʿi subject it can thus be considered a major treatise on the doctrine of the imamate. The Tathbīt al-imāma does not deal with the metaphysical significance of the imamate. Rather, it concentrates on its legal and historical aspects, using proofs derived from the Qurʾān, ḥadīth and logical arguments. in this regard, it is directed at the Islamic public in all its different religious affiliations.

In the way it discusses the necessity of the imamate itself, the right of the imams to the vicegerency of the Prophet, and the validity of divine designation in contrast to election by the umma, it is likely that the Tathbīt al-imāma could have also meant to serve as a guide book for the Ismailis in legitimising the ʿAlid state ruled by the Fatimid Caliph-Imams.

This edition has been compiled from two manuscripts of the Tathbīt, both of which are now in the collections of the library of The Institute of Ismaili Studies, with the Arabic text carefully translated into idiomatic English to retain the character and flavour of the original text as much as possible.