Book excerpt: Health-related behaviours play positive or negative roles in people’s health. For instance, health risk behaviours, such as sedentary behaviours (e.g., binge-watching TV and playing computer games), the use of alcohol, tobacco, or other substances, and lack of sleep, have been found to negatively affect the physical and mental health of people. On the other hand, some studies show that health-promoting behaviours, such as physical activity and healthy dietary habits, can mitigate or reverse the negative effects of health risk behaviours on health outcomes. In the meantime, some studies indicate that the harmful effects of some health risk behaviours may not be mitigated by health-promoting behaviours. For instance, some studies show that sedentary behaviours and physical activity are independently associated with some physical and mental health outcomes; interventions to increase physical activity with and without decreasing sedentary time lead to different health outcomes. Clearly more research is needed to show the interaction between health-promoting behaviours and health risk behaviours in health, which could shed light on the management of health-related behaviours.