This book is a study of the reports of the Einsatzgruppen, the four SS extermination squads that followed in the wake of the German attack on the Soviet Union in June 1941. It was the Einsatzgruppen that began the systematic massacre of Jews and other undesirables. These killings are the principal focus of this book and are analyzed in central chapters from several perspectives. These reports provide a virtually complete and self-contained body of documents and are a fertile source for historians of Third Reich and the Holocaust.