In this chapter, we examine the psychological state of employee work engagement. Our objective is to provide an overview of the engagement construct, clarify its definition, and discuss its behavioral outcomes. We discuss the development of the work engagement construct, which has led to many inconsistencies among scholars about its definition. We clarify that engagement captures employees’ strong focus of attention, intense absorption, and high energy toward their work-related tasks. Work engagement is important to the positive organizational scholarship (POS) field because engagement can lead to a number of positive outcomes, such as in-role and extra-role performance, client satisfaction, proactivity, adaptivity, and creativity. Managers, however, must ensure that employees have adequate resources and sufficient breaks, so that engagement does not lead to burnout or depletion. We encourage scholars interested in studying engagement in the future to investigate the contextual moderators that affect the relationship between engagement and employee behavior and examine the differential effects of the components of engagement—attention, absorption, and energy.