This chapter gives an up-to-date overview of the state-of-the art of research and theorizing regarding work engagement. First, a brief history is presented of the emergence of engagement in business and in academia (section 1), which is followed by a discussion of various definitions that are used in business and in science (section 2). Next it is argued that engagement is a unique construct that can be differentiated, for instance from job related attitudes such as job satisfaction and organizational commitment, and from work addiction and personality dispositions (section 3). Moreover, the most important theoretical frameworks are discussed that are used to explain engagement (section 4) and the organizational outcomes of engagement are elucidated (section 5). The chapter closes with some general conclusions and an outlook on the future of this intriguing psychological state (section 6). Read more.