Obesity is a worldwide epidemic and numerous studies have focused on the identification of its early determinants. The early postnatal period appears to be a critical window of the development of obesity. Early eating patterns and behaviors can determine later eating habits and food preferences. As for obesity, large discrepancies in breastfeeding initiation according to sociocultural characteristics have been highlighted, but less data are available for breastfeeding duration and introduction of complementary feeding. The objectives of this project, named SOFI, are 1/ to provide descriptive national statistics for breastfeeding initiation, breastfeeding duration and complementary feeding practices, 2/ to analyse in details the sociocultural determinants of these feeding practices, 3/ to analyse the influence of these early feeding practices on children’s growth and fat mass, and health in the first years of life, 4/ to collect data on feeding practices in infants from low-income families and to evaluate the first phase of an intervention program designed to improve dietary intakes in this population The present project proposes to gather data from different on-going prospective birth cohorts (ELFE, EDEN and OPALINE), from a qualitative study of families recruited at the same time as the ELFE families, and from the first phase of an intervention study in low-income families (the MALIN project). The work plan of this project has been divided into 5 tasks to carry out the work that will enable: • the socio-cultural determinants of breastfeeding initiation to be identified and the prevalence of breastfeeding initiation in France to be estimated in Task 1; • the socio-cultural determinants of breastfeeding duration to be identified and the distribution of duration of breastfeeding in France to be estimated in Task 2; • the socio-cultural determinants of complementary feeding practices to be identified and these practices described in a French context in Task 3; • the influence of early feeding practices on child’s growth and fat mass to be analysed in Task 4; • the first phase of an intervention trial on infant feeding practices in low-income families to be evaluated in Task 5. Task 6 will deal with the management and administration of the project. A dedicated Task 7 will ensure the synthesis, dissemination and take-up of Tasks 1-5 work and results by stakeholders and in particular policy makers This project will involve five teams with complementary fields of expertise: social sciences, sensory perception and nutrition, epidemiology. Most involved teams have already interacted in the frame of the preparation of questionnaires for the ELFE study since 2005. To encourage interdisciplinarity exchanges within this project, we decided to ask for a post-doctoral fellow on ELFE data, with joint supervision from all academic partners. In the same way, a study engineer will be recruited to prepare ELFE data. Finally, the INED team will be in charge of the transversal axis on geographical factors in early feeding practices. The MALIN partners will actively contribute to the different tasks by bringing their knowledge of the low-income families, their field experience and their network with both local and national organizations in charge of infancy. Through the different partners of the MALIN program, additional synergies with the SOFI partners will be identified and implemented.