Psychology of Physical Activity is a comprehensive and in-depth introduction to exercise psychology, from theories of motivation and adherence to the design of successful interventions for increasing participation. Now in a fully revised and expanded third edition, it is still the only textbook to offer a full survey of the evidence-base for theory and practice in exercise psychology, and the only textbook that explains how to interpret the quality of the research evidence. With international cases, examples and data included throughout, the book also offers the most detailed examination of the relationship between physical activity and mental health of any exercise psychology textbook.