Tracing the Sudden Infant Death Syndrome (SIDS) diagnosis from its mid-century origins through the late 1900s, Rest Uneasy investigates the processes by which SIDS became both a discrete medical enigma and a source of social anxiety construed differently over time and according to varying perspectives. American medicine reinterpreted and reconceived of the problem of sudden infant death multiple times over the course of the twentieth century. Its various approaches linked sudden infant deaths to all kinds of different causes—biological, anatomical, environmental, and social. In the context of a nation increasingly skeptical, yet increasingly expectant, of medicine, Americans struggled to cope with the paradoxes of sudden infant death; they worked to admit their powerlessness to prevent SIDS even while they tried to overcome it. Brittany Cowgill chronicles and assesses Americans’ fraught but consequential efforts to explain and conquer SIDS, illuminating how and why SIDS has continued to cast a shadow over doctors and parents.