Qualitative case study research on Physician Assistants / Background: The Ministry of Health and Long Term Care (MOHLTC) introduced Physician Assistants (PAs) into the Ontario health care system in 2006 to help increase patient access to care, decrease wait times, and improve continuity of care. As a new addition to Ontario, little research exists to describe the roles and contributions of PAs. The aim of this dissertation is to explore PA role integration through an in-depth analysis of setting and role descriptions, barriers and facilitators of role integration, and healthcare provider perceptions. Methods: An exploratory, multiple-case study was used to examine PA role integration in four clinical settings: family medicine, emergency medicine, general surgery, and inpatient medicine. Inductive thematic analysis was used within each of the four cases and for the cross-case thematic analysis. Results: Forty-six health care providers and administrators were interviewed across 19 different healthcare sites. Support for PA contributions across various health care settings, the importance of role awareness, supervisory relationship attributes, and role vulnerability (in relation to sustainability and funding) are interconnected and dynamic in general surgery, inpatient medicine, emergency department and family medicine settings. These findings demonstrate how the flexible and adaptable nature of the PA role and the PAs ability to build relationships allows for the establishment of interprofessional, collaborative, and person-centered care. Conclusions: This dissertation provides a rich understanding of the role of PAs in the Ontario healthcare system through an exploration of role definition, impact on patient care, and professional perceptions. The findings from this dissertation are important from a broad systems perspective as the results help fill existing knowledge and practice gaps regarding the role of PAs, and will help inform the design of human health resource research in order to optimize health care system efficiencies. / Thesis / Doctor of Philosophy (PhD) / Physician Assistants (PAs) are a new health care profession in Ontario, and were introduced by the Ministry of Health and Long Term Care (MOHLTC) in 2006 to help increase access to care and decrease wait times for patients. PAs are trained to work with physicians to extend healthcare services. This research study was undertaken to explore how the PA role has been integrated into number of health care settings, including family practices, emergency departments, general surgery and inpatient medicine settings. The research design is a qualitative case study, which allows for an in-depth exploration of the PA role. Findings revealed that PAs are flexible, collaborative, and adaptable members of healthcare teams in Ontario, who have an interest in enhancing patient care. Despite these benefits, role optimization is often limited by factors such as lack of funding and resistance from other healthcare providers. The findings from this study help fill research gaps around the PA profession in Ontario, and will help inform stakeholders interested in optimizing the impact of PAs in the Ontario healthcare system.