The Tathbit al-imama attributed to the FatimidCaliph-imam al-Manur (334-341/946-953) is animportant early ismaili treatise on the legitimacy of theimamate of Ali b. Abi Talib and that of the ismailiimams from among his progeny. As one of the earliestismaili works on this crucial and fundamental Shi'isubject it can thus be considered a major treatise onthe doctrine of the imamate.The Tathbit al-imama does not deal with the metaphysicalsignificance of the imamate. rather, itconcentrates on its legal and historical aspects, usingproofs derived from the Quran, Hadith and logicalarguments. in this regard, it is directed at the islamicpublic in all its different religious affiliations.in the way it discusses the necessity of the imamateitself, the right of the imams to the vicegerency of theProphet, and the validity of divine designation incontrast to election by the umma, it is likely that theTathbi al-imama could have also meant to serve as aguide book for the ismailis in legitimising the Alidstate ruled by the Fatimid Caliph-imams.This edition has been compiled from two manuscriptsof the Tathb?t, both of which are now in the collectionsof the library of The institute of ismaili Studies, withthe Arabic text carefully translated into idiomaticEnglish to retain the character and flavour of theoriginal text as much as possible.