A well-resourced, comprehensive, population-based set of strategies is needed to attenuate and eventually reverse the current trends of increasing obesity prevalence now apparent in most countries. The Epidemiological Triad (host, vector, environment) has proven to be a robust model for other epidemics and is applied to obesity. Host-based strategies are primarily educational and these tend to be most effective among people with higher incomes and higher educational attainment. The main vectors for a high-energy intake are energy-dense foods and drinks and large portion sizes and, for low energy expenditure, machines that promote physical inactivity. Vector-based strategies that alter food formulation can have a significant impact, particularly through influencing common, high-volume foods. The increasingly 'obesogenic' environments are probably the main driving forces for the obesity epidemic. There are many environmental strategies that can influence the physical, economic, policy or socio-cultural environments, but the evidence base for these potentially powerful interventions is small. Children should be the priority population for interventions, and improving the general socio-economic conditions for disadvantaged, marginalized or poor population sectors is also a central strategy for obesity prevention. The key settings for interventions are schools, homes, neighbourhoods, primary health care services and communities. The key macroenvironments for interventions are the transport and infrastructure sector, the media and the food sector.