The Youth Smoking Survey (YSS) is a classroom-based survey of a representative sample of schools in the ten Canadian provinces. When first administered in 1994, it was the largest and most comprehensive survey on youth smoking behaviour since 1979. The YSS was repeated in 2002 and 2004 in order to track changes in the attitudes and behaviour of Canadian children and adolescents with respect to tobacco. Previously, YSS was only administered to students in grades 5 through 9. In the 2006-07 YSS, the survey was extended to include all secondary students in a province (i.e., grades 5 to 12 in most provinces and in Quebec, Primaire 5, 6 and Secondaire I to V). The 2006-07 YSS was coordinated by Centre for Behavioural Research and Program Evaluation (CBRPE) and the SHAPES team (School Health Action, Planning and Evaluation System) at the University of Waterloo. Data were collected during the fall, winter, and spring of the 2006-07 school year. The main objective of the YSS is to provide benchmark data on national prevalence rates for students in grades 5 through 12. In addition, it provides a unique opportunity to advance our knowledge of the psychosocial correlates of smoking behaviour, including initiation and cessation. Further, it can assist in exposing individual differences in the influence of tobacco marketing, purchasing controls, and other policy initiatives. YSS offers a detailed snapshot of purchasing behaviour, knowledge and awareness of warning labels, and information about the effect of continued tobacco marketing. This information is critical to assessing the need for increased legislative controls on tobacco, and bolstering public support for these policy options. Without this type of monitoring, the effectiveness of our prevention efforts cannot be gauged.