This project analyses how social epigenetics –the study of biological pathways through which social environments become embodied– modifies the analysis of the social determinants of health. It investigates the epistemic uncertainty and social uses of an emerging science which provides “biosocial” models for health: 1- Does social epigenetics socialize biological factors or does it biologize the social? Does it redefine the boundaries between the social and natural sciences? 2- Do professionals and policy-makers make use of research findings in epigenetics? Our methodology is mostly qualitative. It will be applied to the study of six research programs with policy implication, in Europe and in the United-States, which show the different scientific contexts and public health issues of social epigenetics.