Mental well-being is a critical element of total health. There is a spectrum of mental states that range from clinically diagnosed psychopathologies such as depression and schizophrenia to total wellness that might be represented by constructs such as high self-esteem, subjective well-being, and life satisfaction. This module critically examines the evidence underpinning the role of physical activity in a) the avoidance of mental disorders, b) recovery from mental disorders, and c) the well-being and quality of life of those with or without mental disorders. The module will also address the definition and measurement of key psychological constructs that act as markers of psychological well-being. Initiatives to enhance mental health through physical activity will be discussed and implications for health service design and delivery will be identified.