Studies of religious belief and psychological health are on the rise, but most overlook atheists and agnostics. We review 14 articles that examine differences between nonbelievers and believers in levels of psychological distress, and potential sources of distress among nonbelievers. Various forms of psychological distress are experienced by nonbelievers, and greater certainty in one's belief system is associated with greater psychological health. We found one well-documented source of distress for nonbelievers: negative perceptions by others. We provide recommendations for improving research on nonbelievers and suggest a model analogous to Pargament's tripartite spiritual struggle to understand the stresses of nonbelief.