This paper outlines the National Institute for Health and Clinical Excellence's (NICE) emerging conceptual framework for public health. This is based on the experience of the first 3 years of producing public health guidance at NICE (2005-2008). The framework has been used to shape the revisions to NICE's public health process and methods manuals for use post 2009, and will inform the public health guidance which NICE will produce from April 2009. The framework is based on the precept that both individual and population patterns of disease have causal mechanisms. These are analytically separate. Explanations of individual diseases involve the interaction between biological, social and related phenomena. Explanations of population patterns involve the same interactions, but also additional interactions between a range of other phenomena working in tandem. These are described. The causal pathways therefore involve the social, economic and political determinants of health, as well as psychological and biological factors. Four vectors of causation are identified: population, environmental, organizational and social. The interaction between the vectors and human behaviour are outlined. The bridge between the wider determinants and individual health outcomes is integration of the life course and the lifeworld.