Depression in adolescence is associated with poorer outcomes than adult-onset depression. While effective treatment can prevent difficulties from persisting into adulthood, current interventions for adolescent depression are often limited in effectiveness, likely because they fail to address the specific mechanisms underlying depression during this developmental stage. Effective, practical, and targeted treatments are urgently needed. To achieve this, we must identify key mechanisms of adolescent depression and develop interventions that address them directly. Growing evidence highlights reward function as a key mechanism in adolescent depression. At the same time, research suggests that Behavioral Activation (BA), with its emphasis on reward-focused behavioral changes, is an effective but understudied treatment for adolescents with depression. While the National Institute for Health and Care Excellence called for research looking specifically at BA in adolescents with depression in 2019, the evidence base for BA in this group is still underpowered. To integrate emerging research across neuroscience, psychology, and clinical practice, we used a narrative approach to synthesize cross-disciplinary literature on reward function and BA in adolescent depression. This review found evidence for the effectiveness and feasibility of BA in adolescents. However, the mechanisms through which BA works in adolescence are still largely unknown, and questions remain on its optimal delivery, with the review identifying tensions in the cross-disciplinary literature. Further research is needed to clarify how reward function influences both adolescent depression and response to BA, as well as how adolescents themselves wish to engage with BA therapy, so that optimal treatments can be designed.