PROJECT SUMMARY/ABSTRACT Heat waves are a growing public concern and a leading cause of climate-related morbidity and mortality in the US. Eight out of 10 U.S. population live in urban areas. The combination of rising temperatures and urbanization poses a significant risk for vulnerable urban populations due to the slow release of heat by urban heat islands created by extreme summer temperatures. While adaptation planning for heat waves during the day has been developed and implemented at the city-wide and governmental levels, heat adaptation behaviors in individual households are less understood, particularly during nighttime hours. Although prior studies have identified several individual factors associated with heat adaptation, the role of nighttime indoor heat exposure as an external hazard has not been examined. Moreover, the contribution of the built environment on heat exposure and individual adaptation behavior has not been fully evaluated although the build environment play a role in residential household. To fill these gaps, we will examine the combined effects of individual factors, built environment, and nighttime indoor heat exposure on heat adaptation behavior using the Protective Action Decision Model. The long-term goal of this study is to reduce heat exposure risks and increase resilience to climate change for vulnerable urban populations. Our aims are to establish a community advisory board and examine the effects of indoor home heat exposure, individual attribute, and built environmental factors on heat adaptation behavior. The study results will be disseminated to community leaders and residents. We expect that disseminating our findings regarding the drivers and barriers of heat adaptation behavior helps individuals living in underserved urban communities take the necessary steps to reduce their potential health risks associated with nighttime heat exposure. We believe that the results of this study can provide an affordable and practical adaptation strategies for those affected by heat exposure during nighttime. This proposed exploratory study is directly responsive to the National Institute of Environmental Health Science Strategic Goal 2: Promoting Translation- Data to Knowledge to Action: Emerging Environmental Health Issues (Climate Impacts on Health and Preparation for Future Threats) and has the potential to reduce heat exposure risks and increase resilience to climate change for vulnerable urban populations.