In 2010, the National Institute of Mental Health launched the Research Domain Criteria (RDoC). The RDoC seeks to enhance research on the "active ingredients" of mental health concerns, and conceptualizes these concerns as disorders of neural circuitry. A key focus of the RDoC involves understanding mental health across biopsychosocial domains that traverse traditional diagnostic categories, such as impairments in affect, cognition, regulatory systems, and social processing. The RDoC advanced a framework for understanding these impairments as they manifest across multiple "units of analysis": measured variables for which activity reflects functioning across biopsychosocial systems (e.g., subjective reports, behavioral performance, neural activity, cellular assays). However, scholars whose work focuses on children and adolescents encounter challenges with adopting the RDoC's units of analysis framework, which requires a developmental adaptation. In particular, 50 years of research points to a key reality: the RDoC's units of analysis will yield low correspondence, and this low correspondence will translate to inconsistent research findings. Yet, no guidelines exist for interpreting low correspondence among these units or integrating them for research purposes. Prior work on clinical assessments of children and adolescents points to theoretical and methodological models that facilitate interpreting and integrating multi-source assessments. In this introductory article to an RDoC-informed Special Section, we discuss how researchers might apply these models to interpreting and integrating the RDoC's units of analysis using a developmental perspective. This Special Section reveals new lines of RDoC-informed research, particularly the development of paradigms for "strategically" integrating activity from multiple units of analysis. [This paper was published in "Journal of Clinical Child and Adolescent Psychology" v49 p279-296 May 2020.]