East West Street weaves together legal history and personal detective work as Philippe Sands uncovers the origins of two world-changing concepts: genocide and crimes against humanity. Sands, a professor of international law who has argued cases before international courts, began by researching the Nuremberg trials and discovered that the prosecutors who invented these legal categories—Hersch Lauterpacht and Raphael Lemkin—had both studied in the same city, Lemberg (now Lviv), where Sands's own grandfather was born. The book follows Sands as he traces his family history while simultaneously exploring how Lauterpacht and Lemkin developed competing frameworks for addressing Nazi atrocities. Crimes against humanity focuses on individual victims; genocide addresses the destruction of groups. The tension between these approaches continues to shape international law. Sands interweaves his personal investigation—discovering the fate of relatives who perished in the Holocaust—with the intellectual history of human rights law, creating a work that is simultaneously family memoir, legal scholarship, and historical reconstruction. The book's multiple strands converge in Nuremberg, where Hans Frank, the Nazi governor of Poland who ordered the destruction of Sands's family, faced justice under laws created by survivors of the very persecutions he perpetrated.