Background:In 2015, the College of Family Physicians of Canada (CFPC) expanded its Certificates of Added Competence (CAC) program to include enhanced-skill certification in Care of Elderly, Family Practice Anesthesia, Palliative Care, and Sports and Exercise Medicine. We aimed to describe the impact of these 4 CACs on the provision of comprehensive care in Canada, while also identifying the factors of influence that foster these impacts.Methods:Between September 2018 and June 2019, we conducted qualitative case studies of 6 family medicine practices across Canada, sampled to represent geographic, population and practice arrangement diversity. We developed a framework of relevant factors and their relations to CAC-mediated comprehensive care delivery. We took an exploratory approach to the first 4 case studies, guided by theoretical propositions based on a literature review, and the CFPC’s 4 principles of family medicine and goals for practice. The emerging theory was confirmed and adapted through the final 2 explanatory case studies. Data were obtained through semistructured qualitative interviews with enhanced-skill and generalist physicians, specialists, trainees and administrators associated with these cases. We performed a descriptive content analysis, within and across cases.Results:Interviews with 48 participants showed considerable variation in the way CACs are operationalized related to the specific domain of care, the community, relationships among practitioners, motivations of the practitioner and needs of the patient population. The presence of CAC holders in communities expands the scope of available services, reduces the need for patients to travel and encourages continuity of care; however, comprehensive care may be negatively affected when CAC holders develop enhanced-skill practices according to clinical interests rather than community needs. Factors associated with collaborative care models, practice requirements, remuneration structure, community culture and individual aspirations interact to reinforce or undermine the effectiveness of enhanced-skill practices.Interpretation:Holders of CACs have a positive impact when they work in collaborative models that align with the needs of communities and that support local generalist family physicians. Health care policies should incentivize CAC activities that contribute to planned care delivery at the practice and community levels.