Abstract The following Master’s Thesis provides a theoretical and empirical investigation, syn-thesis and discussion of psychological maltreatment (PM) as a possible developmental psychopathological risk factor. Within a developmental and ecological framework, im-portant conditions for child development are described including the complex social systems surrounding the child, the caregiver-child-relation, and children’s basic needs. Psychological maltreatment is hereafter theoretically and empirically evaluated as a possible developmental risk factor in relation to the described developmental conditions and needs. The overall aim of this thesis was to investigate and discuss the possible developmental psychopathological consequences of childhood exposure to PM. Objective: To systematically review and synthesize evidence for the association be-tween childhood PM and subsequent psychopathological outcomes, in accordance with the PRISMA 2020 Statement. Methods: Systematic literature searches with customized search strategies were con-ducted in four electronic databases (Embase, PsycInfo, ProQuest & PubMed). To be eligible, longitudinal cohort studies had to investigate self-reported and/or agency-reported childhood PM in association with later psychiatric symptomatology and/or mental disorders. Study quality and risk of bias were assessed using the Newcastle-Ottawa Scale. Study characteristics and findings are presented in tables, followed by a narrative synthesis of the results. Results: 12 reports, of moderate to high study quality, were included in the qualitative synthesis comprising 9 longitudinal cohort studies and data on 23126 children and youth, mainly located in the U.S., Australia and Europe. Childhood PM was associated with a two- to three-fold increased risk of subsequent mental disorders. Childhood PM significantly predicted depression (OR = 1.6-5.9), anxiety (OR = 1.4-2.8), PTSD (OR = 2.2-4.3), internalizing (OR = 1.6-3.1) and externalizing (OR = 1.6-2.9) behavior as well as substance abuse (OR = 2.1). Non-suicidal self-harm and behavioral disorders were also significantly predicted by PM. Discussion: Evidence was limited by potential selection bias, confounding variables, attrition bias, potential recall- and social desirability-bias, as well as potential missing data, due to reporting barriers among professionals. The qualitative synthesis’ sensi-tivity, specificity and validity is challenged by definitional and operational disagree-ments, in terms of exposure ascertainments. Generalizability of findings are also lim-ited. Synthesized evidence highlights childhood PM as a prevalent and serious devel-opmental risk factor for subsequent psychopathology and underlines the need for both preventative and early interventional strategies. This association, as possibly mediated by neuro-physical, psychosocial and multi-/equifinal mechanisms, is discussed. The systematic review has important implications for the psychological field and prac-tice. There is an urgent need to recognize and acknowledge PM as a global threat to children’s developmental outcomes and future mental health. Development of shared definitions and operationalizations of PM, as well as prioritized training and education of professionals, in identification, assessment and intervention of PM, are crucial. In-creased political, public and societal focus on promoting positive and appropriate care-giving practices is also necessary. Further research should strive to identify causes, mediating factors and consequences of childhood PM in relation to a lifelong and ac-cumulating exposure to stressors and protective factors. Population-based intervention-al studies are also needed to further assess and evaluate the effectiveness, and possible improvement of, current strategies for prevention and intervention of children and youth exposed to, or in risk of being exposed to, PM. A global effort, cooperation and prioritization of child protection and welfare is of utmost importance.