In Western societies, lifestyles now represent one of the most significant predictors of health, or conversely, disease. Multiple authors (for example, Omran 1971; Cockerham 2007; Hinote and Wasserman 2013) carefully outline many recent social and epidemiological transformations in these societies, and lifestyles emerge from these shifts with renewed prominence in health matters. Theorists, researchers and practitioners conceptualise the term "lifestyle' in various ways, but health lifestyles are of particular theoretical and empirical significance for medical sociologists and social epidemiologists. However, a comprehensive theoretical framework that specifically articulates the roles and mechanisms of these important health phenomena did not exist until the early twenty-first century, with the work of American medical sociologist William Cockerham (2005). This chapter provides a thorough background, explication and application of Cockerham's health lifestyles theory, which effectively accounts for the interplay of the individual and their inextricable connections to social structures, and demonstrates the value of critically applying core sociological concepts to the typically individualistic concept of lifestyle.