How can we prevent drug use among young people? This issue provides an overview of the levels of use of various psychoactive substances and presents the analyses and practices of 20 expert professionals (psychiatrists, educators, psychologists, etc.). A 36-page feature. Also in this issue: a series of articles on obesity prevention in France, featuring a contribution by A. Basdevant (head of the nutrition department at Hôtel-Dieu Hospital in Paris) and a presentation of the work of five pilot networks for the management of childhood obesity (Lyon, Toulouse, Doubs, Gironde, and Île-de-France). Also in this issue: an interview with anthropologist Sylvie Fainzang on the delicate doctor-patient relationship.