Ray Pawson's realist review method was used to analyse 22 evaluations/reviews of the Moving to Opportunity (MTO) housing intervention. MTO was a randomized controlled trial that moved families from high-poverty to low-poverty neighborhoods in five US cities between 1994 and 2006. This realist review focussed on mental health outcomes of families who moved, as well as the mechanisms through which moving influenced mental health. It identified and assessed the effectiveness of the underlying theory driving MTO, and suggests revising the existing theory. This realist review suggests that, even when moves are voluntary, there are potentially negative mental health outcomes from these types of social interventions. Directing resources towards the improvement of existing communities is one way of improving health outcomes for all community residents.