How can we write a comprehensive, transnational history of the Porrajmos--one that captures the cumulative nature of anti-Gypsy persecution across Germany, Austria, and Switzerland from 1870 to 1945? The Nazi Genocide of the Sinti and Roma Peoples: A Transnational History traces the evolution of policies targeting the so-called 'Gypsies,' moving beyond national boundaries to reveal a shared regional logic of exclusion and biopolitical control. While Holocaust historiography has long focused on the genocide of European Jews, the Porrajmos--the genocide of the Sinti and Roma--has only recently been recognized as a distinct history of systematic suffering and destruction. However, no existing work fully addresses the transnational continuities and ruptures that shaped this persecution. Drawing on extensive German, Austrian, and Swiss archival research, and framed by Michel Foucault's concepts of biopolitics and thanatopolitics, this book examines the shifting treatment of Sinti and Roma communities. It highlights the transition from liberal assimilationist policies during the Kaiserreich to the radical racial extermination under Nazi rule. The study also uncovers how Nazi Germany extended its genocidal policies beyond its borders, coordinating with Austria and Switzerland--most notably through the International Criminal Police Commission (ICPC), a precursor to Interpol. Finally, this book reveals the complexities of Nazi collaboration, showing Austria's complicity in the genocide, while Switzerland adopted policies of sedentarization and exclusion rather than mass murder. The Nazi Genocide of the Sinti and Roma Peoples offers a critical new perspective on the Porrajmos as both a product of national regimes and a transnational project of racialized state violence.