The authors review evidence regarding the biological processes that may link religiosity/spirituality to health. A growing body of observational evidence supports the hypothesis that links religiosity/spirituality to physiological processes. Although much of the earliest evidence came from cross-sectional studies with questionable generalizability and potential confounding, more recent research, with more representative samples and multivariate analysis, provides stronger evidence linking Judeo-Christian religious practices to blood pressure and immune function. The strongest evidence comes from randomized interventional trials reporting the beneficial physiological impact of meditation (primarily transcendental meditation). Overall, available evidence is generally consistent with the hypothesis that religiosity/spirituality is linked to health-related physiological processes--including cardiovascular, neuroendocrine, and immune function--althogh more solid evidence is needed.