The ambulatory diagnostic process is potentially complex, resulting in faulty communication, lost information, and a lack of team coordination. Patients and families have a unique position in the ambulatory diagnostic team, holding privileged information about their clinical conditions and serving as the connecting thread across multiple healthcare encounters. While experts advocate for engaging patients as diagnostic team members, operationalizing patient engagement has been challenging. The team science literature links improved team performance with shared mental models, a concept reflecting the team's commonly held knowledge about the tasks to be done and the expertise of each team member. Despite their proven potential to improve team performance and outcomes in other settings, shared mental models remain underexplored in healthcare. In this manuscript, we review the literature on shared mental models, applying that knowledge to the ambulatory diagnostic process. We consider the role of patients in the diagnostic team and adapt the five-factor model of shared mental models to develop a framework for patient-clinician diagnostic shared mental models. We conclude with research priorities. Development, maintenance, and use of shared mental models of the diagnostic process amongst patients, families, and clinicians may increase patient/family engagement, improve diagnostic team performance, and promote diagnostic safety.