Background and aims: Children in out-of-home care have usually experienced significant adversity in their lives, which may negatively affect their behavioral development. Problem behavior among children in out-of-home care are of particular concern given children's history of adverse caregiving as well as trauma resulting from maltreatment and system involvement, presenting increased risk of maladjusted problem behavior trajectories. Interventions have been developed to address this problem, but systematic reviews of the evidence find that understanding of interventions that work best for different subgroups of children is currently limited. Despite difficulties, some children in out-of-home care still make positive behavioral adjustment. Research suggests that understanding the processes underlying problem behavior development and identifying risk and protective factors that may benefit particular subgroups is needed (Shpiegel, 2016). This thesis speaks to this gap in the literature by investigating behavioral risk and protective factors for children in out-of-home care. Methods: This thesis comprises two studies. First, a systematic literature review (Study 1) of risk and protective factors for the longitudinal development of problem behavior for children in out-of-home care was conducted. It aimed to identify variables that have been examined in existing literature and provides evidence of risk or protective effects that may be targeted in behavioral interventions. The second study analyzed longitudinal secondary data, the National Child and Adolescent Well-Being (NSCAW) I, on the problem behavior outcomes of 513 children who have been in long-term out-of-home care in the United States (Study 2). Specifically, the study used multiple-group latent growth curve models to explore whether there were any risk or protective correlates and factors for problem behavior development. Moderated mediation path analyses were then carried out to understand the specific relationship between severity of recent incident of abuse, caregiver involvement, responsibility skills, post-traumatic stress symptoms, and problem behavior outcomes 36 months later. Findings. Study 1 identified and synthesized 146 studies, which indicated that children's longitudinal behavior development is associated with a wide range of factors (individual characteristics, interpersonal relations, interventions, etc.). Challenges related to synthesis of heterogeneous methodologies, contexts, and findings were also highlighted. Findings: from Study 1 also informed the statistical approach of Study 2, by identifying variables that are key in the child welfare literature, as well as identifying gaps in the research that require further investigation. In Study 2, analyses identified several variables to be statistically associated with behavior problems. The identified variables were: type of caregiver (permanent/non-permanent), age at initial placement, daily living skills, school engagement, neighborhood community environment, trauma symptoms, caregiver involvement, socioemotional skills, and severity of recent abuse incident. Path analyses revealed that caregiver involvement and responsibility skills were not affected by recent incident of abuse, but significantly decreased later problem behavior outcomes, suggesting a protective relationship that buffers against the adverse effects of maltreatment experience. Conclusion: This thesis presents evidence that several individual and contextual characteristics may be risk and protective variables for children who have been in long-term out-of-home care, and that these variables vary according to children's age. Such findings suggest the need for future research and practice to consider children's ages to efficiently carry out research and provide services. Findings also highlighted the significant gap in the child welfare literature, suggesting that socioemotional skills are not well understood for children with long-term out-of-home care histories, and sheds light on how these variables can be studied further in the future. These findings may also inform future interventions to promote positive behavioral adjustment of children in out-of-home care, by identifying variables that correlate with positive or negative change over time.