Although psychologists were certainly not the first to study flourishing, virtues, spirituality, and religiousness, one of their key contributions has been to examine these constructs using the scientific method. Complex concepts such as gratitude, humility, spirituality, and religiousness present unique challenges to researchers, requiring them to utilize equal doses of scientific rigor and methodological ingenuity. In this chapter, we describe some of these efforts in both positive psychology and the psychology of religion/spirituality (R/S). Specifically, we provide examples of research using correlational cross-sectional data, longitudinal data, experiments, field research, and qualitative and mixed methods. We then discuss the strengths and weaknesses of using each approach to study positive psychological and religious/spiritual constructs. We note some advances in technology that may open new directions for research, and we discuss future directions for the fields, including issues of research transparency and the need for cross-cultural research.