This paper will examine the legitimizing ideology of the Fatimid dynasty from the time of the establishment of their first state in Ifriqiyya (Tunisia) in 297 H/909 CE, to the transfer of their state to Egypt in 356/969. The establishment of an Isma'ili Shi`i empire in the 10th century, while remarkable, was also challenging for the Fatimids, who had proclaimed themselves initially, imams of the Isma`ili Shi`a. As such they had led a movement that constituted a revolutionary alternative to the Abbasid dynasty, and the oppositional politics of the Fatimid mission or da'wa certainly appealed to a broad range of subject peoples of the Abbasid dynasty. The Shi`i nature of the Fatimid movement nevertheless potentially exacerbated latent Sunni-Shi`i tensions often encouraged by the Abbasids themselves, and more importantly posed a problem on achieving power. Whether to rule as imams, or as caliphs, and even as the latter, to avoid alienating their own followers, non-Shi`i Muslims, and non-Muslims in their multi-confessional empire is a debate and struggle reflected in particular in the amans, or guarantees of safety, issued by their agents and generals to conquered people. Through them, we can chart an evolution in the way the Fatimids deployed their identity as Shi`i imams and Muslim rulers to legitimize their rule to a variety of audiences. The amans are preserved in Fatimid texts such as the Iftitah al-da`wa, the Kitab al-majalis wa'l-musayarat, and later histories such as al-Maqrizi's Itti`az al-hunafa', which will be examined here. Drawing on the concepts of batin (esoteric or inner) and zahir (exoteric or public) and the relationship between the two that were articulated and popularized by the fifth generally recognized Shi`i imam, Muhammad al-Baqir, the Fatimids negotiated a co-existence of loyalty to themselves as imams by the Isma'ili community, and acceptance of themselves as caliphs by the non-Ismaili majority they came to rule. This policy enabled the Fatimids to gain acceptance of their subject peoples for the two and a half centuries of their rule, even if it ultimately left their Isma'ili subjects vulnerable to the Sunnification campaigns of subsequent dynasties such as the Ayyubids of Egypt and Syria. At the same time, their formulation of a dual role as imam and caliph, challenges our own notions of a consensus regarding the Islamic nature of the caliphate