A large body of nonexperimental literature finds residing in a disadvantaged neighborhood is deleterious for mental health, and recent evidence from the Moving to Opportunity (MTO) program—a social experiment giving families living in high-poverty neighborhoods the opportunity to move to low-poverty neighborhoods—suggests a causal effect of moving to a low-poverty neighborhood on adult mental health. We use qualitative data from 67 Baltimore adults who signed up for the MTO program to understand how moving to a low-poverty neighborhood produced these mental health benefits. First, we document the vast array of mental health challenges, traumatic experiences, and stressors reported by both experimentals (those who received a housing voucher to move to a low-poverty neighborhood) and controls (those who did not receive a voucher). We then explore how changes in the physical and social environments may have produced mental health benefits for experimentals. In particular, experimentals reported the following: improved neighborhood and home aesthetics, greater neighborhood collective efficacy and pride, less violence and criminal activity, and better environments for raising children. Notably, we also document increased sources of stress among experimentals, mostly associated with moving, making the positive effects of MTO on adult mental health all the more remarkable. These findings have important implications for both researchers and policymakers.