Many researchers have concerns about work engagement's distinction from other constructs and its theoretical merit. The goals of this study were to identify an agreed-upon definition of engagement, to investigate its uniqueness, and to clarify its nomological network of constructs. Using a conceptual framework based on Macey and Schneider (2008; Industrial and Organizational Psychology, 1, 3–30), we found that engagement exhibits discriminant validity from, and criterion related validity over, job attitudes. We also found that engagement is related to several key antecedents and consequences. Finally, we used meta-analytic path modeling to test the role of engagement as a mediator of the relation between distal antecedents and job performance, finding support for our conceptual framework. In sum, our results suggest that work engagement is a useful construct that deserves further attention.