This thesis looks at how and why 'lifestyle' (understood as diet, exercise and other health behaviours) became the primary focus of public health in post-war Britain. It uses Britain's biggest killer - heart disease - as a lens through which to view this paradigm, tracing lifestyle's development from its roots in risk-factor epidemiology, through health promotion campaigns, to its embedment in the practices of everyday life. Lifestyle’s origins in post-war social medicine and epidemiology are explored through two case studies. Firstly, the identification of physical inactivity as a risk factor, and how exercise was reinvented as a preventive health activity, consciously practiced to compensate for sedentary working lives. The second explores how research on sugar, a putative risk factor for heart disease, was unsuccessful, with its nutritional, rather than epidemiological, approach. Such epidemiological research was translated into the political and policy spheres via the consensus for prevention that developed in 1970s. This viewed lifestyle as a means of halting the rise of non-communicable diseases such as heart disease, and the concomitant burden that they placed on the welfare state. Lifestyle was conceived as a set of practices that individual citizens were encouraged to perform as a quid pro quo for the continuation of the NHS free at the point of delivery. This focus on personal responsibility continued into the 1980s, as a major campaign on heart disease tried to persuade a sceptical public to exercise and eat healthily. In doing so, it appealed to Thatcherite values of self-reliance and family values, suggesting a confluence between lifestyle public health, neoliberalism and social conservatism. However, an explicitly class-based analysis of public health also emerged concurrently. Health inequalities research, specifically the Whitehall studies, disrupted the lifestyle paradigm, highlighting the structural determinants of health and suggesting an alternative narrative for public health in Britain.