The International Tracing Service, one of the largest Holocaust-related archival repositories in the world, holds millions of documents that enrich our understanding of the many forms of persecution during the Nazi era and its continued repercussions ever since. Drawing on a selection of recently available documents from the archive, this essential resource provides new insights into human decision-making in genocidal settings, the factors that drive it, and its far-reaching consequences. The sources that the author has collected and contextualized here reflect the full range of behaviors and roles that victims, their oppressors, beneficiaries, and postwar aid organizations played beginning in 1933, through World War II, the Holocaust, and up to the present.