Contemporary post-editing process research studies have measured temporal, technical, and cognitive post-editing effort, often using eye tracking to measure the latter. Many of these studies use fixation duration and fixation count as a proxy for cognitive effort. The number of participants is usually small, and each study has a different focus, making results difficult to compare directly. This chapter provides a review of many of these studies, and then addresses some practical difficulties in running such studies. Post-editing remains a contentious activity for many translators, and eye-tracking studies of the process are a useful way to make the interaction with machine translation more acceptable to users.