Introduction: The Oral Case Presentation (OCP) has been described as a unique form of inter-physician communication integral to the practice of medicine and represents the foundation of trainee-supervisor interactions. In recent years, entrustment has been identified as an essential element of trainee supervision and learning. Despite the growing body of knowledge concerning entrustment in medical education, the influence of trust on the educational dynamic surrounding the OCP remains unknown. The objectives of this study were to (1) describe the complex nature of the OCP from the perspective of the supervisor and (2) explore the central role the OCP plays in the dyadic relationship between supervisor and trainee during the delivery of patient care. Methods: Using a constructivist grounded theory approach, semi-structured interviews were conducted from 2015 to 2016 with a purposive sample of attending Emergency Medicine (EM) physicians from the University of Ottawa. Transcripts were reviewed independently by two investigators using line-by-line coding and constant comparative analysis. Emerging concepts were coded and key themes identified through consensus. Theoretical sampling occurred until thematic saturation was reached. Results: Twenty-one attending EM physicians participated in this study (71% male). The mean number of years in practice was 14. The mean percentage of shifts with a trainee assigned was 86%. Factors relating to entrustment were identified as the principal influences on both the content of the OCP and decisions relating to trainee supervision during the OCP process. These factors included the trainee level, the trainee-supervisor relationship, the context and the task. The OCP was also found to play several important roles as supervisors balanced the delivery of patient care and trainee education. These roles were related to communication, teaching and trainee assessment. Conclusion: The OCP represents a core activity within the supervisor-trainee relationship in which trust plays a central role. Clinical supervisors value the OCP as a form of authentic assessment of skills and perceive it to be a key determinant in making entrustment decisions. Future studies designed to evaluate the utility of the OCP as an educational tool should consider entrustment as an essential element.