Religion and spirituality (R/S) are central aspects of human experience, both now and throughout history, that could have direct and indirect implications for health processes and outcomes. Although difficult to define, and therefore difficult to measure, religion and spirituality are overlapping concepts that also have distinct qualities. A currently agreed-upon definition is that ‘spirituality will be defined as one’s experiences with the sacred, whereas religion refers to one’s involvement in an organized system of beliefs and behaviors related to one’s experience with the sacred’ (Yeary et al. 2020: 196). Self-report measures of R/S have dominated the empirical study of R/S and health with the unidimensional measure of religious service attendance being pre-eminent. However, R/S are conceptualised as multidimensional constructs with individual dimensions showing significant interrelationships. Conceptual overlap between measures of R/S and health has presented the potential for methodological confounding when studying relations between R/S and health, and should be carefully attended to during study design. The existing empirical literature suggests that, in general, there is a beneficial relationship between R/S and objectively measured physical health outcomes, which has been investigated regarding several dimensions of health and illness. However, the specific association varies depending on the population studied, aspect of R/S measured, and specific health outcome. Currently, the strongest evidence is found when religious service attendance is the R/S variable and all-cause mortality is the outcome. The size of this relationship appears to be about the same as that for recognised health behaviours. There is some evidence that service attendance predicts cardiovascular- and cancer-specific mortality as well, although aspects of R/S other than service attendance may also have important relations. Similarly, R/S appear to be associated with cardiovascular morbidity, with positive religious coping being the most consistent predictor of beneficial outcomes, and with religious struggle or negative religious coping predicting adverse outcomes in cardiovascular populations. The research is not clear concerning cancer. Less is known about what R/S-relevant mechanisms may account for these relations, though the most commonly investigated, with varying levels of support, include social support, meaning and purpose, religious orientation (intrinsic/extrinsic), self-regulation and health behaviours, virtues, and positive/negative emotionality. Clearly, more systematic research is needed in each of these areas. Though R/S have existed worldwide throughout history, and therefore may have adaptive qualities embedded within them, careful empirical study of R/S and health remains deficient. This leaves health-care practitioners often unaware of the existing literature and uncertain about how to regard this important aspect of human functioning when it comes to health. Nevertheless, it seems clear that R/S organisations are prominent sources of social support that have evident benefits for their members. Further, R/S organisations may be trusted sources of health information and accepted places for health-screening campaigns, particularly among underserved and minority populations. R/S communities may be bound by their shared world view, understanding of meaning/purpose, and emphasis on behavioural self-regulation. Better understanding of how these and other aspects of R/S can be used in the service of improved health is needed.