Adults living in high-poverty neighborhoods often fare worse than adults in more advantaged neighborhoods on their physical health, mental health, and economic well-being. Although social scientists have observed this association for hundreds of years, they have found it difficult to determine the extent to which the neighborhoods themselves affect well-being versus the extent to which people at greater risk for adverse outcomes live in impoverished neighborhoods. In this article, we examine neighborhood effects using data from the 10- to 15-year evaluation of the Moving to Opportunity (MTO) for Fair Housing demonstration, which offered randomly selected families a housing voucher. The experimental design of MTO allows us to isolate the effects of neighborhoods from selection bias. We find that, 10 to 15 years after enrolling participants, the program had very few detectable effects on economic well-being but had some substantial effects on the physical and mental health of adults. For adults whose families received the offer of a housing voucher that could be used to move only to a low-poverty neighborhood, we find health benefits in terms of lower prevalence of diabetes, extreme obesity, physical limitations, and psychological distress. For adults offered a Section 8 voucher, we find benefits in terms of less extreme obesity and lower prevalence of lifetime depression.