In the Jewish case, mass migration is typically associated with the large migration wave from East to West, i.e. from Eastern to Western Europe and, in the main, to the United States during the period 1870-1920. Three other Jewish mass migrations also had a major impact in the modern era after 1500: The expulsion-edict of the Spanish crown against Jews (and Muslims) in 1492 triggered a large migration of Sephardic Jews to the Maghreb, the Ottoman Empire, and to a lesser degree to Northwest Europe and into the Atlantic hemisphere. Since the late Middle Ages large groups of Jews moved, often fleeing violent persecution, from Central to East Central Europe, primarily to Poland, Lithuania, Galicia and the Ukraine. During the 20th century the so called Alijahs to Palestine/Israel constituted the most recent significant Jewish mass migration. Jews constitute a Diaspora 'in exile' with different shifting centers: Spain, Poland/Lithuania, Russia, Iraq, Germany and, more recently, the United States, and since the early 20th century, Palestine and later Israel. Focusing on the impact of Jewish mass migrations after 1500, the author wants to shed light on the question how, against the background of migration, Jews negotiated unity and difference within the Jewish group and without, regarding the social and political context at large: 1. The long-term impact of mass migrations within the (enlarged) Jewish group in the destination regions. This point raises in particular the question how Jews bridged their differences sustaining communities, often under pressure from without, by the state and society. 2. Jewish mass migrations and the transition from Empire to Nation: While Jews as a group fared best in large multi-ethnic Empires like the Ottoman or the Austro-Hungarian Empires and, interestingly, in the United States of America, the situation was much more difficult, even precarious, in states that pushed homogeneity, and in particular after 1933/1939 with the implementation of the anti-Semitic German annihilation policy. The most interesting case is represented by Jewish migrants moving from the Russian and Austro-Hungarian Empires to the United States.