Theoretically, purpose serves as a basic dimension of healthy psychological functioning and an important protective factor from psychopathology. Theory alone, however, is insufficient to answer critical questions about human behavior and functioning; we require empirical evidence that explores the parameters of purpose with respect to measurement, prediction, and modification. Here, we provide empirically supported insights about how purpose can operate as a beneficial outcome (e.g., marker of well-being), a predictor or mechanism that accounts for benefits that a person derives (such as from an intervention), or a moderator that offers insight into when benefits arise. Advancing the study of purpose requires careful consideration of how purpose is conceptualized, manipulated, and measured across the lifespan. Our aim is to help scientists understand, specify, and conduct high-quality studies of purpose in life.