John Schulenberg as a developmental scholar and mentor: Personal reflections.

John Schulenberg has had significant impact on developmental science. His conceptual writing and empirical research, grounded in developmental contextualism, emphasized the critical role that developmental transitions play in shaping health risks, especially substance use, across the life course. Schulenberg's integration of developmental concepts with large-scale epidemiological studies, particularly through his leadership in the Monitoring the Future study, provides key insights into how significant life changes-such as school transitions, employment, and relationships-interact to influence well-being across adolescence and early adulthood. He was a fierce advocate for adolescence and young adulthood being critical phases of life, deserving of focused attention and support. John was also a devoted mentor to the next generation of developmental scientists. This commentary reflects on John Schulenberg's legacy, highlighting five of his foundational concepts (developmental tasks, transitions, trajectories, turning points, and timing) and celebrating his role as a generative and joyful mentor. He fostered open intellectual dialog, promoted and celebrated career development, and took pleasure in life inside and outside work, helping early career scientists to develop innovative and impactful research programs. Schulenberg's commitment to positive relationships and celebrating success is an enduring model for future generations of developmental scientists and mentors.