This chapter explores task engagement as a construct relating to how individuals focus on, interact within, and learn from tasks in the language classroom. The chapter first defines task engagement and provides a brief overview of existing work on the topic. This review shows that task engagement is the level and quality of a learner’s integrated mental and physical activity, as well as their affective experience, within a task. The chapter then compares task engagement with task motivation, another framework for looking at students’ involvement in task-based language learning. The chapter ends with suggestions and ideas for task engagement research that treats individuals’ task engagement as a holistic, situated, adaptive, and momentary phenomenon. The stance taken throughout the chapter is that confusion in understanding task engagement may arise when macro-level information (i.e., general engagement tendencies in a collective of learners across a course of task-based language learning) is used to capture micro-level insights about the time (momentary), task (an individual task), and agent (the individual learner). The chapter proposes ways to reconfigure the unit of analysis and the level of granularity at which task engagement is conceptualized, observed, and measured.