From their common roots in Human Factors Engineering, Human-Centered Design and Cognitive Systems Engineering have drifted into distinct fields over the past three decades, each developing beneficial heuristics, design patterns, and evaluation methods for designing for individuals and teams, respectively. GeoHAI, a clinical decision support application for preventing hospital-acquired infection, has yielded positive results in early usability testing and is expected to test positively in supporting joint activity, which will be measured through the novel implementation of Joint Activity Monitoring . The design and implementation of this application provide a demonstration of the possibilities and necessities to unify the work of Human-Centered Design and Cognitive Systems Engineering when designing technologies that are usable and useful to individuals engaged in joint activity with machine counterparts and other people. We are calling this unified process Joint Activity Design, which supports designing for machines to be good team players.