Despite the importance of religion in many college students' lives, little is known about how religious affiliation is associated with student growth and development. This study examines the relationship between college students' religious affiliations and well-being using a longitudinal sample of 14,527 students at 136 institutions. Analyses show that students who do not identify with any religious affiliation have reduced well-being compared with mainline Christian students. Moreover, engaging in religious activities and attending an institution with an inclusive religious climate are associated with greater gains in well-being. Implications for practice and future research are discussed. (Contains 3 tables.)