In September 1939 part of Eastern Poland was incorporated into the Soviet Union under the terms of a secret protocol drawn up between Molotov and Ribbentrop. A central issue in this crucial episode of East European history is the extent to which the Jews in the area collaborated in the imposition of Soviet rule, how they learned to live under a new system, and how a new culture evolved. But in the summer of 1941 the Red Army retreated from the region in the face of German invasion, and close behind the German army came the Einsatzgruppen, the mobile death units. This is an important moment in the history of the Holocaust which is subjected to detailed examination in Ben-Cion Pinchuk"s book.