The Centre for Addiction and Mental Health’s Ontario Student Drug Use and Health Survey (OSDUHS) is the longest ongoing school survey of adolescents in Canada, and one of the longest in the world. The OSDUHS has been conducted every two years since 1977, and 2017 marks the study’s 40th anniversary. A total of 11,435 students in grades 7 through 12 from 52 school boards, 214 schools, and 764 classes participated in the 2017 OSDUHS, which was administered by the Institute for Social Research, York University. This report describes the past year use of alcohol, tobacco, illicit drugs, nonmedical (NM) use of prescription drugs, and other substances of concern, and changes since 1977. Also examined are harms related to drug use, perceptions and attitudes, and exposure to drugs. All data are based on self-reports derived from anonymous questionnaires administered in classrooms between November 2016 and June 2017.