Project Summary Smoke-free housing (SFH) has recently been mandated by the U.S. Department of Housing and Urban Development (HUD) to protect public housing residents from secondhand smoke (SHS) exposure. However, our preliminary work suggests that SFH might not be effective. In focus groups, smokers in low-income housing have reported to us that they are primarily motivated by fear of punishment, rather than an obligation to comply with SFH, which they perceive to be unfair. They describe a situation in which many smokers respond by hiding their smoking inside their apartments?where they think they will be less likely to be seen?when compliance with SFH is perceived to be an inconvenience or even unsafe (e.g., if they would have to walk across their community at night to smoke off the property). This suggests that the perceived legitimacy of SFH is low?residents feel so strongly about its unfairness that they are unlikely to comply with it on their own. This means that efforts to increase resident compliance by relying on threats of punishment could be counterproductive. Residents also report several barriers to compliance with SFH that they also perceive to be unfair (e.g., banning smoking in public housing but allowing it on other types of properties). These barriers vary between housing authorities and represent important differences in SFH implementation strategy. Principles and approaches from community-based participatory research guide this study. In Aim 1 we assess factors associated with perceived legitimacy and compliance across six housing authorities. We will use a mixed methods approach to establish: (1) who exhibits lower perceived legitimacy of SFH, and under what circumstances, and (2) what property and organizational factors that differ between and within housing authorities could affect SFH implementation and resident compliance. In Aim 2 we test associations between perceived legitimacy, SFH implementation strategy, and several markers for SHS (fine particulate matter, airborne nicotine, and exhaled CO). We hypothesize that: (a) perceived legitimacy will be related to differences in SFH implementation, (b) differences in SFH implementation strategy will affect SFH compliance, as measured by SHS, and (c) low perceived legitimacy of SFH will mediate the impact of implementation strategy on SFH compliance. In Aim 3 we develop a scalable implementation strategy for SFH that to improve resident compliance and perceived legitimacy. Community advisory boards will be used to inform this process to ensure that solutions are grounded in real-world experiences.