This chapter provides a state-of-the-art overview on the assessment of work engagement. First the conceptualization of work engagement is critically discussed, followed by a review of studies on the assessment of the construct. It is estimated that the Utrecht Work Engagement Scale (UWES) is used in over 85% of all academic papers on engagement of employees. It is concluded form a host of psychometric studies that the UWES is psychometrically sound instrument with sufficient factorial validity, factorial invariance, internal consistency, stability, and discriminant validity. Moreover, the content validity of the UWES is demonstrated in many studies as well, for instance showing that work engagement is positively associated with challenging demands, job resources and personal resources. Moreover, it predicts attitudinal and behavioral outcomes such as commitment, workability, and sickness absence, as well as business outcomes such as productivity, service performance, and financial success. Finally, work engagement as assessed with the UWES also predicts health and well-being outcomes such as, cardiovascular health, life satisfaction, and non-occurrence of depression. Also, alternative work engagement questionnaires with more limited application are discussed (download full paper).