Cannabinoid use and cannabinoid use disorder (CUD) are widespread and have a host of negative consequences. CUD shares many features with other substance use disorders, such as tolerance and withdrawal, that have been studied at length. Cannabinoid use is also associated with several key mental health conditions of high interest to patients and clinicians alike. This chapter will examine many aspects of cannabinoid use and CUD, including the most recent epidemiology, developmental risk factors, neurobiology, diagnosis, clinical features, and co-morbidity with conditions such as depression, schizophrenia, and other substance use disorders. Discussion of these issues in relation to adolescents and adults will appear throughout, given the unique role cannabinoid use has in young people. This chapter will also explore recent updates in these areas sparked by changes in cannabinoid policy found in certain geographic regions. Analysis of trends in CUD will extend beyond smoking cannabis to include vaping and use of other cannabinoid products such as synthetic agonists.