In this project, we will develop a behavioral economics module within the Constances epidemiological cohort in order to measure patient’s individual economic preferences toward risk, ambiguity and time. These psychological variables and the associated biases are the cornerstones of the normative and descriptive models of individual health decisions in health and behavioral economics. In WP1, we will administratively and logistically set up, implement and include an innovative behavioral economics module on individual preferences within the Constances cohort. We will conduct a web-based questionnaire to an online representative sub-sample of Constances volunteers in two waves at a one-year interval. Our aim is to collect a repeated measure of individual preferences of 5000 Constances volunteers. We will link this module to Constances survey data and medical records as well as relevant data from the French national security database (SNIRAM). We will hire specifically for this project a data manager and a data scientist (for respectively 24 and 18 months) who will prepare the dataset and preliminary statistics and will assist the scientific teams in charge of the four research projects presented hereafter. In WP2, we will investigate the evolution of individual preferences in a life course perspective and more precisely the causal and selection effects linking socioeconomic position to individual preferences (WP2.1) and the role of the patient’s health history in the evolution of individual preferences over time (WP2.2). In WP3, we will examine how individual preferences and socioeconomic indicators (SEP and economic insecurity) jointly determine individual choices of health-related behaviors in terms of primary prevention (e.g. over-eating, poor diets, lack of physical activity, smoking, alcohol abuse, drug use, sleep deprivation) and of secondary prevention (in particular for breast and cervical cancer screening) (WP 3.1) and of decisions related to pollution exposure and residential area (WP 3.2). The results of these studies will inform public policy makers on the decision making process involved in individual health-related behaviors and the social inequalities in health they can induce. Also, the unique dataset resulting from the BeHealth project will constitute a precious public good for national or international researchers in health economics, medicine, epidemiology and public health interested by the concepts developed in behavioral economics on individual preferences and deviations (or biases) from economic rationality.