Gambling problems impact 0.2%-4.0% of the population, and research related to treating gambling has burgeoned in the last decades. This article reviews trials for psychosocial treatments of gambling problems. Using Preferred Reporting Items for Systematic Reviews and Meta-Analyses Standards, we identified 21 randomized trials. Eleven studies evaluated interventions delivered via multisession, in-person therapy: cognitive therapies, cognitive-behavioral (CB) therapies, and motivational interventions (MI) alone or with CB therapies. An additional 10 studies used approaches that involved 1 or fewer in-person sessions; these included workbooks with CB exercises alone or in combination with MI and brief feedback or advice interventions. Although most studies found some benefits of CB therapy (alone or combined with MI) and brief feedback or advice relative to the control condition in the short term, only a handful of studies demonstrated any long-term benefits. Nearly half the studies used waitlist controls, precluding an understanding of long-term efficacy, and standardized outcomes measures are also lacking. Populations also differ markedly across studies, from nontreatment-seeking persons who screened positive for gambling problems to those with severe gambling disorder, and these discrepant populations may require different interventions. Although problem gamblers with less pronounced symptoms may benefit from very minimal interventions, therapist contact generally improved outcomes relative to entirely self-directed interventions, and at least some therapist contact may be necessary for patients with more severe gambling pathology to benefit from CB interventions. As treatment services for gambling continue to grow, this review provides timely information on best practices for gambling treatment.