Transactional models employing cross-lagged panels have been used for over 40 years to examine the longitudinal relations and directional associations between variables of interest to child and adolescent mental health. Through a narrative synthesis of the literature, we provide an accessible overview of cross-lagged panels with attention to developing a research question, study design and assumptions, dynamic effects (including the random-intercept cross-lagged panel model), and reporting and interpretation of results. Implications and critical appraisal guidelines for readers are discussed throughout. Overall, several key points are highlighted, with particular emphasis on the intended level of inference, model and measure selection, and timing of assessments. Despite limitations in establishing causation, cross-lagged panel models are fundamental to non-experimental epidemiologic research in child mental health and development.