This study examines how perceptions of the legitimacy of university sustainability efforts--support by the administration (authorization) or from students' peers (endorsement)--as well as the physical context in which students live, matter in shaping students' environmentally responsible behaviors (ERBs). Using survey data collected from fourth-year students at a university in the Southeastern US, we employ Seeming Unrelated Regression to analyze the impact of perceived legitimacy and context on recycling and conservation behaviors, controlling for demographic characteristics, pro-environmental attitudes, and environmental identity. Our findings indicate that students' perceptions of what university administrators support affect the likelihood of students to enact recycling and conservation behaviors, and peer support influences conservation behaviors. This research contributes to the literature on legitimacy by examining how legitimacy processes work in natural, rather than experimental, settings.