Children in foster care have high rates of adverse childhood experiences and are at risk for mental health problems. These problems can be difficult to ameliorate, creating a need for rigorous intervention research. Previous research suggests that intervening with children in foster care can be challenging for several reasons, including the severity and complexity of their mental health problems, and challenges engaging this often transitory population in mental health services. The goal of this article was to systematically review the intervention research that has been conducted with children in foster care, and to identify future research directions. This review was conducted on mental health interventions for children, ages 0 to 12, in foster care, using ERIC, CINAHL, PsycINFO, PubMed, ProQuest's Dissertation and Theses Database, Social Services Abstracts, and Social Work Abstracts. It was restricted to interventions that are at least "possibly efficacious" (i.e., supported by evidence from at least one randomized controlled trial). Studies were evaluated for risk of bias. Ten interventions were identified, with diverse outcomes, including mental health and physiological. Six interventions were developed for children in foster care. Interventions not developed for children in foster care were typically adapted to the foster context. Most interventions have yet to be rigorously evaluated in community-based settings with children in foster care. Little research has been conducted on child and family engagement within these interventions, and there is a need for more research on moderators of intervention outcomes and subgroups that benefit most from these interventions. In addition, there is not consensus regarding how to adapt interventions to this population. Future research should focus on developing and testing more interventions with this population, rigorously evaluating their effectiveness in community-based settings, determining necessary adaptations, and identifying which interventions work best for whom.