ABSTRACT Currently, only 40% of dementia can be explained by known risk factors and individual-level interventions have been largely ineffective in preventing illness. As a result, there is increasing attention on aspects of the physical environment that may have a role in poor cognitive functioning in later life and the development of Alzheimer’s disease and related dementias (ADRD). While air pollution is a known risk factor for dementia, the impacts of other aspects of the natural environment on brain health are less well studied. Notably, extreme temperatures have been linked to increased thermal discomfort, disrupted sleep, poorer mental health, as well as accelerated neuron degeneration and nervous system damage, yet there is very little research on the impacts of temperature on the aging brain. This project will leverage the substantial aging research infrastructure of the Gateway to Global Aging Data project to promote research on the impacts of extreme temperatures on cognition and dementia. By conducting analyses in surveys from the United States, Mexico, and India, we will help to establish methodology and guidance documents that can be used by the larger Health and Retirement Study and its International Network of Studies (HRS-INS) research community and advance the science on extreme temperatures and health. Specifically, our aims are to: 1) Quantify the associations of exposures to extreme heat and cold over long time frames with cognitive function and dementia prevalence in older adults; 2) Investigate the degree to which extreme heat and cold over short time frames are associated with cognitive function in older adults and evaluate sources of susceptibility; and 3) Generate guidance documentation for climate research in the Gateway and share these resources with the broader research community. This proposed research is highly innovative because it examines both short- and long- term exposure to extreme temperatures on cognition and dementia prevalence within the Gateway project, leveraging intra- and international sources of variation for added power and better generalizability to an economically diverse set of nations. Additionally, given the richness of data in the Gateway project, we will be able to newly examine sources of susceptibility at the individual level to better understand how extreme temperatures impact cognitive health and the subpopulations most affected. Lastly, we will help to establish methodology and guidance documents that can be used by the larger HRS-INS research community and advance the science on extreme temperatures and health.