The built environment has significant direct and indirect effects on mental health. High-rise housing is detrimental to the psychological well-being of women with young children, and poor-quality housing increases psychological distress. Design elements that affect social interaction, such as furniture configuration and privacy, impact the mental health of psychiatric patients. Alzheimer's patients fare better in smaller, homely facilities with lower stimulation and accommodations for physical wandering. Residential crowding and loud external noise sources elevate psychological distress but do not cause serious mental illness. Malodorous air pollutants and certain toxins (e.g., lead, solvents) can cause behavioral disturbances and negative affect. Insufficient daylight is associated with increased depressive symptoms. Indirectly, the physical environment influences mental health by altering psychosocial processes with known mental health consequences, such as personal control, social support, and restoration from stress and fatigue. More prospective, longitudinal studies and randomized experiments are needed to examine these relationships. The task of developing underlying models of how the built environment affects mental health is challenging, and some individuals may be more vulnerable to these impacts, particularly those from low-income and ethnic minority backgrounds. The article critically analyzes the direct and indirect effects of the built environment on mental health, highlighting the need for better understanding of the psychosocial and biological processes that link the built environment to mental health.The built environment has significant direct and indirect effects on mental health. High-rise housing is detrimental to the psychological well-being of women with young children, and poor-quality housing increases psychological distress. Design elements that affect social interaction, such as furniture configuration and privacy, impact the mental health of psychiatric patients. Alzheimer's patients fare better in smaller, homely facilities with lower stimulation and accommodations for physical wandering. Residential crowding and loud external noise sources elevate psychological distress but do not cause serious mental illness. Malodorous air pollutants and certain toxins (e.g., lead, solvents) can cause behavioral disturbances and negative affect. Insufficient daylight is associated with increased depressive symptoms. Indirectly, the physical environment influences mental health by altering psychosocial processes with known mental health consequences, such as personal control, social support, and restoration from stress and fatigue. More prospective, longitudinal studies and randomized experiments are needed to examine these relationships. The task of developing underlying models of how the built environment affects mental health is challenging, and some individuals may be more vulnerable to these impacts, particularly those from low-income and ethnic minority backgrounds. The article critically analyzes the direct and indirect effects of the built environment on mental health, highlighting the need for better understanding of the psychosocial and biological processes that link the built environment to mental health.