As nation-states make greater efforts to regulate the flow of people on the move—refugees, economic migrants, and international travelers alike— advocates of DNA profiling technologies claim DNA testing provides a reliable and objective way of revealing a person’s true identity for immigration procedures. This article examines the use of DNA testing for family reunification in immigration cases in Finland, Germany, and the United States—the first transatlantic analysis of such cases—to explore the relationship between technology, the meaning of family, and immigration. Drawing on our analyses of archival records, government documents, and interviews with immigration stakeholders, the authors argue that DNA testing is not conclusive about the meaning of family. While the technology may facilitate decision making for both would-be immigrants and state officials, this study shows hesitancy among the latter to let DNA testing make the final determination. The authors introduce the concept of social validity—whether the interpretation of test results matches social or political meanings in a given local context—in order to make sense of the complexities and challenges of DNA testing in practice. They show that DNA testing is not just a technology of belonging or a way to claim citizenship rights. It may also enable exclusion and denial of rights.