This book traces the origins of modern varieties of Yiddish and presents evidence for the claim that, contrary to most accounts, Yiddish only developed into a separate language in the 15th century. Through a careful analysis of Yiddish phonology, morphology, orthography, and the Yiddish lexicon in all its varieties, Alexander Beider shows how what are commonly referred to as Eastern Yiddish and Western Yiddish have different ancestors. Specifically, he argues that the western branch is based on German dialects spoken in western Germany with some Old French influence, while the eastern branch...