Recent advancements in sensing techniques for mHealth applications have led to successful development and deployments of several mHealth intervention designs, including Just-In-Time Adaptive Interventions (JITAI). JITAIs show great potential because they aim to provide the right type and amount of support, at the right time. Timing the delivery of a JITAI such as the user is receptive and available to engage with the intervention is crucial for a JITAI to succeed. The goal of this project is to evaluate the various factors that affect users’ receptivity to JITAIs, and develop learning algorithms to potentially predict such opportune moments. To answer the different research questions, we conduct several field studies where participant receive different types mHealth interventions.