This paper examines three broad waves in the evolution of the psychology of religion and spirituality over the past 50 years toward a field that integrates theory, research, and practice. In the first wave, researchers attempted to demonstrate the interconnectedness of religion with various aspects of human functioning. However, this research was largely correlational, relied on global measures of religiousness, and failed to identify what it is about religious life than may affect behavior. In the second wave, researchers began to integrate religious research into mainstream psychological theories and examine religious life in more of its richness and complexity. The field experienced a dramatic upsurge in study in part due the rise of interest in the construct of spirituality. The second wave produced findings that were ripe for application. In the third wave, researchers and practitioners are currently designing and evaluating ways religious and spiritual resources, problems, and struggles can be integrated into clinical practice. The paper concludes by considering some of the challenges that will need to be addressed as the psychology of religion and spirituality evolves further toward an empirically-based applied field.