How people think has a major influence on physical health. Research on placebo effects and mindsets has shown that expectations about outcomes can lead to neurobiological responses in the absence of active treatment. The common-sense model of self-regulation is a framework to understand how people interpret, react to, and manage current and future health threats. Many health behaviour theories exist to identify beliefs that predict why people do or do not engage in health and risk behaviours. Patient beliefs are necessary for shared medical decision-making. Although cognitive heuristics and biases can lead to medical error, decision aids and interventions to increase patient activation can be used to promote more informed decision-making. Stress has a major impact on health, and reappraisal interventions can be used to modify maladaptive thoughts and reduce the negative effects of health. Personality traits and individual differences also influence health outcomes. Research and health care guided by the biopsychosocial model – in which health is determined not only by biological but also by psychological and social factors – can facilitate longer and happier lives.