Where do East European Jews - about 90 percent of Ashkenazi Jewry - descend from? This book conveys new insights into a century-old controversy. Jits van Straten argues that there is no evidence for the most common assumption that German Jews fled en masse to Eastern Europe to constitute East European Jewry. Dealing with another much debated theory, van Straten points to the fact that there is no way to identify the descendants of the Khazars in the Ashkenazi population. Using a multidisciplinary approach, the author draws heavily on demographic findings which are vital to evaluate the conclusions of modern DNA research. Finally, it is suggested that East European Jews are mainly descendants of Ukrainians and Belarussians. UPDATE: The article "The origin of East European Ashkenazim via a southern route" (Aschkenas 2017; 27(1): 239-270) is intended to clarify the origin of East European Jewry between roughly 300 BCE and 1000 CE. It is a supplement to this book.