For decades, psychologists have been interested in the question whether, and how, religious and spiritual behavior, in terms of beliefs, attitudes, practices, and belonging, could be scientifically studied and assessed in terms of their relative good, or ill, for human well-being. This article considers contributions of religious commitment and spiritual practice to well-being and cognitivedevelopmental theoretical models and related bodies of empirical and clinical research regarding religious and spiritual development across the life cycle, with particular attention to questions related to positive adult development.