This volume traces the development of the Jewish calendar from its origins until it reached, in the 10th century CE, its present form. Drawing on a wide range of literary, documentary, and epigraphic sources, this is the first comprehensive book to have been written on this subject. Stern shows that the Jewish calendar evolved during this period from considerable diversity (a variety of solar and lunar calendars) to unity. This consolidation of the calendar is one element in the unification of Jewish identity in later antiquity and the early medieval world.