Researchers commonly rely on adolescents' and parents' reports to assess family functioning (e.g., conflict, parental monitoring, parenting practices, relationship quality). Recent work indicates that these reports may vary as to whether they converge or diverge in estimates of family functioning. Further, patterns of converging or diverging reports may yield important information about adolescent adjustment and family functioning. This work is part of a larger literature seeking to understand and interpret multi-informant assessments of psychological phenomena, namely mental health. In fact, recent innovations in conceptualizing, measuring, and analyzing multi-informant mental health assessments might meaningfully inform efforts to understand multi-informant assessments of family functioning. Therefore, in this Special Issue we address three aims. First, we provide a guiding framework for using and interpreting multi-informant assessments of family functioning, informed by recent theoretical work focused on using and interpreting multi-informant mental health assessments. Second, we report research on adolescents' and parents' reports of family functioning that leverages the latest methods for measuring and analyzing patterns of convergence and divergence between informants' reports. Third, we report research on measurement invariance and its role in interpreting adolescents' and parents' reports of family functioning. Research and theory reported in this Special Issue have important implications for improving our understanding of the links between multi-informant assessments of family functioning and adolescent adjustment.