Problem, research strategy, and findings: Supportive built environments for walking are linked to higher rates of walking and physical activity, but little is known about this relationship for socioeconomically disadvantaged (e.g., low-income and racial/ethnic minority) populations. We review 17 articles and find that most show that the built environment has weaker effects on walking and physical activity for disadvantaged than advantaged groups. Those who lived in supportive built environments walked more and were more physically active than those who did not, but the effect was about twice as large for advantaged groups. We see this difference because disadvantaged groups walked more in unsupportive built environments and less in supportive built environments, though the latter appears more influential. Takeaway for practice: Defining walkability entirely in built environment terms may fail to account for important social and individual/household characteristics and other non–built environment factors that challenge disadvantaged groups, including fear of crime and lack of social support. Planners must be sensitive to these findings and to community concerns about gentrification and displacement in the face of planned built environment improvements that may benefit more advantaged populations. We recommend five planning responses: Recognize that the effects of the built environment may vary by socioeconomics; use holistic approaches to improve walkability; expand walkability definitions to address a range of social and physical barriers; partner across agencies, disciplines, and professions; and evaluate interventions in different socioeconomic environments