Depending on the definitions placed on deaths or casualties that resulted from warfare or crimes against humanity by historians, the figures will vary across resources.
Within Poland, the IPN (Polish Institute of National Remembrance) places their estimated war dead between 5.6 and 5.8 million people. Current estimates now show that the number of war dead within the postwar borders total 26.6 million individuals. Since the collapse of the Soviet Union, there has been a significant amount of research conducted regarding the topic of World War 2 casualties with the resulting opening of previously closed scholarly resources. History of Accounting for the War Dead from World War 2