This volume deals with three themes: medieval Judaism, Arabic and Hebrew sociolinguistics, and Arabic Bible translation. Within Medieval Judaism, the Karaite Jews became a prosperous community under the banners of Islam. One of the most salient signs of the Karaite community's strength and internal cohesion was the extensive scientific contribution that it made to the fields of Biblical studies, Hebrew philology and philosophy. This book presents for the first time a critical edition of one of the works of the leading Karaite scholars in biblical exegeses and translation, Japheth ben Ali's Judaeo-Arabic translation of the "Book of Jeremiah", drawing on five medieval manuscripts. As the majority of Karaite works, including Bible manuscripts, are in Judaeo-Arabic, relatively few of them have been published. A number of the Karaite Bible manuscripts were written in Arabic script, resulting in their being neglected by scholars, despite the significance of these manuscripts to the history of medieval Judaism and Bible textual Studies. The author of this volume focuses on some of the most important issues in the field of sociolinguistics, namely language-contact, diglossia and the status of both Arabic and Hebrew in the medieval Jewish literary system. Equally important is the issue of the script-in-use (Hebrew or Arabic), which was a major subject of debate among the Rabbinates and the Karaites. Indeed, the language and the script used in these manuscripts will help us re-evaluate the established theories about the language-situation and literary systems in medieval Islamic and Jewish societies. The value of translating the Hebrew Bible into Arabic was unparalleled in medieval inter-religious scholarship. For Muslim scholars it was their only access to the Jewish Bible. The contribution of the Karaites to this field is enormous, and this work offers us a unique window into the Karaite theory of Biblical hermeneutics.