INTRODUCTION Th is chapter provides a defi nition of brief interventions and charts their development both empirically and in terms of their theory base. Evidence is set out regarding the eff ects of brief interventions on substance use, including alcohol, tobacco, cannabis, stimulants, benzodiazepines, opiates and multiple substance use. For each of these substances the evidence of the eff ect of brief interventions on mental health-substance use concerns is presented.