Are you working with extremely advanced system, or highly trained and experienced users? In these situations, it can be impossible to fully understand the users’ goals, tasks, and strategies in the time available. Since this understanding is an important component of most usability testing, it may be necessary to approach testing differently. In this session, we’ll present our recent experience conducting usability tests of very complex systems designed for highly trained users. We’ll talk about the challenges we faced, such as how to (1) pick tasks for the test, (2) determine the appropriate level of training for participants, (3) staff and moderate the tests, and (4) identify problems and solutions when you can’t fully understand the tasks. We’ll share our experiences and invite attendees to share theirs as well.