In his 1955 survey of Jewish-Arab relations, 'Jews and Arabs: Their Contacts through the Ages,' S.D. Goitein, a leading scholar of Jewish history in the Medieval Islamic lands, gives almost no attention to the Later Islamic Middle Period (thirteenth-fifteenth century). In fact, Goitein concluded that in the thirteenth century “Arabs faded out from world history, and Oriental Jews from Jewish history.” Thus, he did not consider the history of Jews in the Islamic lands to be of any significance until the modern era (starting in 1800, according to his periodization). Islamic and Jewish histories were perceived to be intertwined in the pre-thirteenth century into what Goitein called ‘Jewish-Arab symbiosis,’ an idea that has been much popularized in later scholarship as the ‘Judeo-Muslim symbiosis.’ In this paradigm, Jews and Muslims achieved the highest intellectual, cultural, and scientific achievements due to the tolerant character of the ‘Arab’ Muslim rule, a character that was lost gradually due to the rise to power of non-Arab peoples within the Islamic lands (the Mamluks in Egypt and Syria, and the Almohads in the Islamic West). This dissertation wishes to challenge the ‘decline theory’ regarding Jewish life in the ‘post-classical’ era of Islam through the examination of three treatises from Egypt and the Maghrib. It argues that traditional periodization of Islamic history affected the historiography of Jewish life under medieval Islam, and that by studying the ‘Jewish-Arab symbiosis’ outside the confines of ‘classical’ Islam, a different image of medieval Jewish history could be reconstructed.