This is the Chief Public Health Officer's fourth annual report on the state of public health in Canada. It examines the state of health and well-being of Canadian youth (aged 12 to 19 years) and young adults (aged 20 to 29 years). The report considers many health issues affecting this population such as physical and mental health, injury, sexual and reproductive health and substance use and abuse. By discussing these issues and how they are addressed, the report identifies priority areas for action to maintain healthy transitions of young Canadians into adulthood.