The first epidemiological studies to link lack of physical activity with adverse health outcomes were published in England in 1953—they identified higher rates of cardiovascular events in occupationally sedentary bus drivers and mail sorters than in occupationally active bus conductors and postal delivery workers. The focus in these early epidemiological studies was on the health consequences of inactivity, especially time spent sitting at work. In the 1970s and 1980s, epidemiological studies began to focus on activity, particularly in leisure time, and the vast range of health benefits associated with it. This focus on leisure time physical activity has continued to dominate the field of physical activity and public health research into the 21st century (and indeed forms the raison d’etre for many SMA professionals). We are now starting to focus on understanding and influencing physical activity in all domains of life as we endeavor to reduce the burden of disease and illness attributable to inactivity and overweight in Australia. This presentation will provide a critical overview of the evidence on physical inactivity and adverse health outcomes, from its early focus on sitting at work, through the benefits of leisure time and transport-related activity, to the emerging concept of sedentary physiology. The presentation will introduce a paradigm shift in the way we think about the balance of activity and inactivity in everyday life. Just how much activity will be necessary, and when must it occur, to keep us merry and bright in our old age?