Nicolas Leenaerts is a BAEF Postdoctoral Research Fellow in the Statistical Reinforcement Learning Lab at Harvard University, led by Susan Murphy. He is also a psychiatrist and a cognitive behavioral therapist in training. His research uses supervised machine learning and reinforcement learning to develop Just-in-Time Adaptive Interventions (JITAIs) that can adjust support based on an individual’s changing context. He is particularly interested in applications to mental health, including interventions that target substance use and eating behaviors. By combining clinical training with methodological work, he aims to strengthen how adaptive interventions are designed and evaluated using intensive data streams. As a 2026 MAPCI Fellow, Leenaerts joins a community advancing rigorous methods for intervention development and evaluation in cancer prevention and control.