Humans have believed in gods and spirits since the earliest days of the Holocene, and many people still believe in them today. Although the existence of religious belief has been a human constant, the nature and prevalence of religion has changed dramatically throughout human history. Here we describe the emerging science of religious change. We first outline a multilevel framework for studying religious change drawn from theories of socioecological psychology and cultural evolution. We illustrate this framework with four case studies featuring two ancient religious changes (the rise of punitive religions and doctrinal rituals) and two modern religious changes (the rise of atheism and nontraditional religions). We then review useful methods for examining religious change, including ethnographic coding, agent-based modeling, and time-series analysis. Next, we explore future directions, highlighting the need for predictive forecasts, nonlinear models, and non-Western samples. We also outline ten key questions that need to be answered for a fuller understanding of religious change. (PsycInfo Database Record (c) 2021 APA, all rights reserved).