This document summarizes a guest lecture on simulation modeling. The lecture covered: 1. An introduction of the speaker and their background in healthcare, Lean Six Sigma, and simulation. 2. Examples of how variability in arrival and service times can impact waiting times, even when average arrival and service rates remain the same. 3. An overview of what simulation is and when it is useful to use, such as when averages are not sufficient, processes are complex, and testing changes without implementing them for real. 4. Examples of how simulation has been used for call center optimization and airport terminal modeling projects to reduce costs and improve customer experience.