Among the many topics covered in the 2010 HBSC survey, the use of legal and illegal psychoactive substances is of particular interest. By surveying students at the very moment when some of them are first experimenting with drugs, the survey allows for a detailed examination of these initial experiences. Most surveys of older populations, in fact, must ask respondents to recall and, if possible, date their past experiences, thereby introducing a degree of imprecision linked to memory bias. In the case of drug use, it is particularly interesting to be able to compare the prevalence of use across different generations when studying the trend toward earlier onset of use and its consequences on future consumption patterns. The HBSC survey thus allows us to avoid these memory-related uncertainties and to measure, in a sense, the prevalence of use “in vivo.” Furthermore, the decision this year to survey not only 11-, 13-, and 15-year-old students as in previous years (see the chapter “General Methodology”), but a representative sample of all middle school students, has significantly improved the study. By thus providing a continuum of the spread of the earliest drug use among middle school students, the study proves to be a vital tool for implementing primary prevention initiatives in schools. It ideally complements the national monitoring system for drug use among adolescents. Now, the entire age range from 10 to 18 is covered thanks to the three surveys—HBSC, Escapad, and Espad—whose similar questions and comparable methodologies also ensure excellent comparability. Given the numerous legislative measures implemented since the early 2000s, both in the fight against smoking and against alcohol consumption among young people, the survey offers a perspective on the public policies carried out over the past decade, even if it cannot be considered an evaluation in the strict sense of the term.[excerpt from chapter]