This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book outlines the European framework of family reunification and the reasons for focussing on Austria, Finland and Germany. After that, we spell out the theoretical debates and the methodological challenges involved in researching the use of DNA analysis in three different countries. It situates DNA testing in the context of the Finnish immigration regime in the late 1990s and early 2000s. The implementation of DNA testing in the Finnish immigration administration is analysed on the basis of primary documents and expert interviews. The chapter describes the procedure, and explores some of the implications of DNA testing in family reunification cases in Austria within the given legal framework and political practices. The use of DNA analysis for family reunification generally raises a number of philosophical questions and ethical concerns.