Learner engagement matters, particularly in simulation-based education. Indeed, it has been argued that instructional design only matters in the service of engaging learners in a simulation encounter. Yet despite its purported importance, our understanding of what engagement is, how to define it, how to measure it, and how to assess it is limited. The current study presents the results of a critical narrative review of literature outside of health sciences education, with the aim of summarizing existing knowledge in these areas and providing a research agenda to guide future scholarship on learner engagement in healthcare simulation. Building on this existing knowledge base, we provide a working definition for engagement and provide an outline for future research programs that will help us better understand how health professions' learners experience engagement in the simulated setting. With this in hand, additional research questions can be addressed including: how do simulation instructional design features (fidelity, range of task difficulty, feedback, etc.) affect engagement? What is the relationship between engagement and simulation learning outcomes? And how is engagement related to or distinct from related variables like cognitive load, motivation, and self-regulated learning?