There is growing evidence that self-affirmation – the process of reflecting upon cherished values or attributes – may have implications for health. Postulated effects range from reducing the defensive resistance to unwelcome health-risk information to ameliorating the physiological response to stress. In this, the first detailed review of the literature on self-affirmation and health, we summarise what is known. Self-affirming can increase acceptance of unwelcome health-risk information, especially among those at greatest risk. Self-affirmed participants typically also report more intention to change behaviour postmessage. There is evidence that certain effects of self-affirming may endure. Self-affirmation has also been shown to have beneficial effects on the response to stress. There is, however, currently only limited evidence of actual health-behaviour change following self-affirmation. We discuss reasons for this and consider key research questions for the next phase of research.