This chapter provides a thorough review of existing measures for assessing engagement. I report on what psychometric information is generally available and what is not, and I offer some suggestions for how to decide which measure is best, given a variety of purposes. I also provide information on whether creating one’s own measure is best. Table 6.1 provides a list of existing measures with validity evidence. This chapter also offers a tutorial on psychometrics as a refresher. The intent is to put good measurement at the forefront and encourage the development of better measures of engagement in organizations. Best practices in measurement are not just for research!