The use of tobacco, alcohol and marijuana by teenagers continues to pose a significant threat to the health of many young Canadians. Recent national surveys indicate that 18 per cent of Canadian teens smoke tobacco daily or occasionally and one-third of all teens have tried marijuana more than once, with about eight per cent of teens using it at least once a week. Just over 44 per cent of teens reported drinking one to three times each month, with an additional 17 per cent of teens aged 15 to 17 drinking one to three times a week or more. Despite extensive prevention efforts, the use of these substances appears to have become a somewhat normalized part of adolescence. The goal of Dr. Richardson’s program of research is to improve our understanding of why adolescents are using these substances, and in so doing, facilitate the development of more effective interventions. For example, Dr. Richardson will be using an internet-based web survey to collect information every six months from a large group of adolescents to examine how the influence of known risk factors for substance use, such as peer influences and psychological characteristics related to risk taking, change as the students’ progress through high school. Dr. Richardson hopes this research will enable researchers to identify specific longitudinal patterns (i.e., trajectories) of alcohol, tobacco and marijuana use and examine how the influence of known risk factors change as adolescents progress through the secondary school system. In addition to improving our understanding of the different patterns of substance use, this research will contribute to the development of individually tailored prevention and harm reduction interventions that can be delivered over the internet.