The changing economic reality of the last decades has prompted large movements of people across and within national borders, which, in turn, have given rise to new opportunities and challenges. This volume addresses a number of key aspects of these developments, by bringing together a unique collection of chapters, written by leading scholars from three different disciplines: economics, sociology, and political science. The first part of the book - Economic Change - starts with two case studies: The mass migration from the former Soviet Union to Israel in the early 1990s, and the mass migration from rural to urban areas in China that started in the mid 1990s. The final chapter of the first part provides a thorough introduction and overview into methodologies that can help to address numerous issues faced by researchers working with migration data, of the type underlying the analysis in the first two chapters. The second part of the book - Social Challenge - discusses how societies are shaped by immigration. It investigates the pitfalls of policies that do not take account of the implications for decisions of individual migrants; explores the important aspect of family re-unification and discusses whether society should follow a path towards a multicultural society or a society that forces newcomers to adopt existing cultures. Finally, this volume ponders whether the diversity created through migration impacts negatively on the societal structure of the receiving countries. These chapters together, written by some of the foremost experts in the areas, provide intriguing insights into the complexity of migratory phenomena and the challenges to policy and society at large.