Arwā bint Ahmad (d. 532/1137) ruled in Yemen for fifty-five years. She played an important political role and at the same time occupied the highest rank in the Ismā'īlī religious hierarchy after that of the imam. Her religious policies, particularly her special relations with the Fatimids, led to the transfer of the Fatimid literary legacy to Yemen, and hence to its preservation following the fall of the Fatimid Caliphate. She likewise organized the new structure of the Yemeni Ismā'īlī da'wa, thus contributing to its survival after the fall of the Sulayhid dynasty. The proposed paper investigates Arwā's career from two different angles: the Fatimid Egyptian and the Yemen Ismā'īlī. The main point will be the way they dealt with the fact that she was a female ruler. The Fatimid caliph-imam al-Mustansir first issued a decree stating that to follow her was a religious duty. He then appointed her to the rank of huğğa, the highest after that of the imam, in order to give her rule a more emphatic legitimacy. The Yemeni Ismā'īlī position is best represented in al-Sultān al-Hattāb's religious tract Gāyat al-mawālīd, where he argues that Arwā's female body was no more than a body envelope covering her original male essence. The fact that Arwā was a woman posed a serious problem for both the Fatimids and the Yemeni Ismā'īlīs. In each case they tried to deal with it in a way that suited their political and religious interests.