Advances in digital technologies have created unprecedented opportunities to deliver effective and scalable behavior change interventions. Two-arm randomized controlled trials (RCTs) provide an excellent way to determine whether a digital intervention package is effective. However, this approach is less helpful in providing empirical information that can be used to optimize an intervention to achieve improved effectiveness and efficiency, while maintaining a desired level of economy and/or scalability. This workshop will present the multiphase optimization strategy (MOST), a three-phase methodological framework for optimizing behavioral interventions based on ideas inspired by engineering methods that stress both ongoing improvement of products and careful management of research and implementation resources. The presenters will use case studies to introduce three types of experimental approaches – the factorial design, the sequential multiple assignment randomized trial (SMART), and the micro-randomized trial (MRT) – and explain how the concepts presented can be applied to optimize attendees’ digital interventions.