As the evidence for the value of active learning in STEM classes grows, questions arise about how to implement such approaches to maximize their effectiveness. Definitions of active learning can lead us to believe that if students are doing content-related work in class rather than listening to lecture, their learning will naturally be improved. But research has shown that this is not necessarily the case. Successful active learning strategies in face-to-face classes depend on a multitude of factors, including question and activity design, faculty prompts, student incentives for participation, and group dynamics. In this chapter I discuss what research suggests is a key underlying reason that these factors impact the results of active learning approachestheir effect on the level of students' cognitive engagement. In this chapter, I discuss the ICAP (interactive, constructive, active, passive) framework for student engagement and how it manifests in various active learning formats. This model explains how certain student behaviors during active learning evoke deeper processing of ideas, and thus, lead to better student learning.