Cannabis is the most widely used illicit drug in the world, with the highest rates of use seen in New Zealand, North America and Australia. There is evidence of a decrease in the age of commencement of cannabis use in some developed countries, and a prolongation of risk of initiation to cannabis use beyond adolescence in more recent cohorts of users. Early initiation of cannabis use and regular use during adolescence are particular risk factors for later problematic cannabis and other drug use, as well as mental health problems, delinquency, loss of cognitive capacity and educational achievement, risky sexual behavior and criminal offending. Cannabis use with tobacco complicates treatment for each condition and should be addressed concurrently. Cannabis users often have a long history of use before seeking treatment, and early screening, assessment and treatment are recommended. There are a number of valid and reliable screening and assessment tools now available. Severity of withdrawal is a factor that increases relapse, and pharmacotherapy for withdrawal management is developing rapidly and showing great promise. Finally, a combination of motivational enhancement therapy and cognitive–behavioral therapy alone or within a family systems model are the proven treatment protocols for cannabis use disorder.