Between 1939 and 1945, Nazi genocide claimed the lives of nearly three hundred thousand people diagnosed with psychiatric illness or cognitive deficiencies. Not until the 1980s would these murders, as well as the coercive sterilizations of some four hundred thousand others classified as “feeble-minded,” be officially acknowledged as crimes at all. The Question of Unworthy Life charts this history from its origins in prewar debates about the value of disabled lives to our continuing efforts to unlearn eugenic thinking today.