For at least three decades, policymakers have struggled to promote work among welfare recipients, while continuing to protect these vulnerable families from economic deprivation. At first, work-oriented services were offered on a voluntary basis to a narrow range of recipients. Over time, participation in work-focused activities became mandatory, initially for recipients with no young children and, eventually, for a very broad share of the welfare caseload. MDRC’s pathbreaking welfare studies have provided rigorous evidence at every major stage of this evolving story and on every major programmatic strategy that has been tried.