Exercise is routinely recommended because of its benefits for physical, cognitive, and mental health. It is especially beneficial for older adults due to its potential buffering effects against Alzheimer's disease and related dementias (Luck et al., 2014). However, little is known about how to best encourage older adults to exercise. Based on behavior change theory, different intrapersonal and interpersonal motivational factors are likely to be relevant during the contemplation, action, and maintenance stages of behavior change. Generally, as a result of motivational shifts toward prioritizing positivity and socially meaningful goals with advancing age (Carstensen, 2006), socioemotional aspects of decision making may become more salient and influential for older adults (Mikels et al., 2015; Peter et al., 2011). Our previous work has demonstrated that positive affect (Mikels et al., 2020) and social goals (Steltenpohl et al., 2019) play a critical role in older adults' motivation to exercise, but these two lines of research have not been integrated to date. Recent work indicates that positive affect is particularly beneficial for health when shared in social connections (Fredrickson, 2016; Major et al., 2018), and the proposed work will, for the first time, examine how shared interpersonal positivity may impact exercise decision making and behavior, especially during the contemplation and action/maintenance stages of behavior change. But who are the older adults that benefit the most from exercise in terms of physical, cognitive, and mental health (and should be hence be targeted with messages)? Not all older adults reap the benefits of exercise (Sparks, 2014) and, conversely, sedentary older adults have the most to gain. Overall, the current proposed research program is innovative in its (a) translational application of insights from affective, cognitive, and aging theory and research to understand the antecedents and outcomes of exercise decision making in younger and older adults, (b) conceptualization of both the social and emotional aspects of decision making, (c) development of novel methods for health messaging that incorporate social influences, and (d) novel assessments of the exercise-health link.