A recent systematic review of research on religion and health has found a consistent relationship between religion and better mental health as well as greater social support. There also appears to be a relationship between religious involvement and better physical health, although the mechanism for this effect is poorly understood. One way that religion could impact physical health is through neuroendocrine and immune mechanisms, or psychoneuroimmunology (PNI). This article describes the physiological mechanisms by which the mind affects the body, reviews research substantiating the link between psychosocial processes and immune functioning, and examines the limited research that has addressed the religion-PNI relationship. Gender differences are emphasized.