In this article, we review the research literature on nonreligion, secularity, the nones, and other forms of "religion's other." As a relatively new area of sustained and still growing research activity, with its attendant theoretical and methodological implications continuing to take shape, our focus is on the social science research from the mid-2000s to the present. We consider the challenges of definition and perspective in this line of inquiry, highlight key arguments, and summarize the main findings from empirical studies of nonreligion and its relationship to topics including identity, health, family, and prejudice. After discussing the organizational and social movement aspects of nonreligious communities, as well as related developments in how scholars are studying these communities, we conclude our assessment of the state of this field by proffering questions relevant to both current efforts and whatever future directions are in store for research on religion's other.