Objective: Ways to clinically assess and treat problem gambling evolve as our knowledge about this disorder increases. This paper summarizes current knowledge about treating problem gambling and describes developments in the assessment, psychology, and biology of problem gambling that may be important for treatment. Methods: We reviewed recent published literature reporting advances in the assessment, psychology, and biology of problem gambling. We retained for review only controlled clinical trials in which subjects were randomized to either psychological or pharmacologic treatment. Results: Although several gambling treatments were found to be efficacious, support for any specific treatment modality is still limited. Cognitive-behavioural treatments were most effective. Although diagnostic assessment has improved, there are still very few measures of gambling-related variables. The contribution to gambling of sex, concurrent psychiatric disorders, cognitive distortions, and impulsivity has been described. Evidence implicating decision-making areas of the cortex and disturbances in serotonin and dopamine functioning has been reviewed. Available evidence for a genetic contribution to problem gambling is weak. Conclusions: Improvements in the methodology of gambling-treatment research were discussed to advance the clinical approach to this disorder. Developments in the area of assessment, psychology, and biology of gambling should inform clinical approaches to a greater degree than they currently do. We identified the need to study different types of gambling separately, rather than combining them, as an important goal.