Gambling disorders, including pathological gambling and problem gambling, have received increased attention from clinicians and researchers over the past three decades since gambling opportunities have expanded around the world. This Seminar reviews prevalence, causes and associated features, screening and diagnosis, and treatment approaches. Gambling disorders affect 0·2-5·3% of adults worldwide, although measurement and prevalence varies according to the screening instruments and methods used, and availability and accessibility of gambling opportunities. Several distinct treatment approaches have been favourably evaluated, such as cognitive behavioural and brief treatment models and pharmacological interventions. Although promising, family therapy and support from Gamblers Anonymous are less well empirically supported. Gambling disorders are highly comorbid with other mental health and substance use disorders, and a further understanding is needed of both the causes and treatment implications of this disorder.