Risk reduction and strength enhancement are both necessary strategies to improve outcomes for youth in foster care who have experienced adversity. Decades of research have articulated the negative long-term outcomes of youth in foster care, but less is known about youth-level modifiable protective factors that can be nurtured through intervention to improve well-being. This scoping review was conducted to synthesize the state of the science on proximal, modifiable individual and interpersonal factors that are associated with psychosocial well-being among adolescent youth in foster care. Following rigorous and recommended methods, we systematically searched, selected and synthesized 20 years of peer-reviewed literature focused on 13-19 year olds in foster care. 41 peer-reviewed, quantitative studies met specified inclusion criteria and were included in this review. We charted the data and synthesized our findings in consultation with an advisory group of researchers, practitioners, and youth with lived experience. Overall, the review highlighted key categories of individual factors (individual strengths, psychosocial needs, and developmental skills) and interpersonal factors (relationships with peers/siblings, caregiving adults, and caring adults in the community) that can have protective value and are associated with psychosocial functioning for adolescent youth in foster care. Moreover, when youth have their needs met, increase their skills and develop strengths, it often leads to better outcomes as well as more and/or higher quality relationships with important people in their lives. Similarly, when youth develop and maintain quality relationships, those connections often lead to opportunities to advance their skills, strengths and positive outcomes. The results of this review contribute new insights for research, practice, and policy intended to enhance psychosocial well-being for young people in foster care. Findings also highlight specific individual and interpersonal factors that interventionists might consider as potential targeted mechanisms of change when developing programming for this population. Implications are discussed.