'Here there is no why', Primo Levi was once told by an SS guard at Auschwitz. The history of Auschwitz-Birkenau is well known; what remains less clear is how the single greatest instance of mass murder in human history should be understood. Drawing on a wide variety of new sources including hitherto unknown documents and testimonies, Nicholas Terry describes and analyses the process of mass murder at Auschwitz. Chronicling the evolution of the practice of extinction, this book shows how contingency and improvisation marked out the genocidal course of the 'Final Solution' at Auschwitz-Birkenau. Using the perspectives of both the SS perpetrators as well as the camp inmates forced to participate in the design, construction and operation of the gas chambers and crematoria, the book asks fresh questions about the motivation, meanings and significance of extermination, and the roles of deception and secrecy in making mass murder possible.