Creative and methodologically sophisticated longitudinal research on bidirectionality in parenting and child behavior can shed important new light on the dynamics of behavior-problem development. The articles assembled for this Special Section are at the forefront of efforts aimed at tracing the interplay of parenting behavior and child and adolescent adjustment problems over time. In this commentary, we provide a brief overview of thinking and research on bidirectionality and then highlight key themes and findings reported in these articles. We describe some of the challenges in research on bidirectional processes and offer some recommendations for future research in this area.