The purpose of this study is to understand the perspectives of primary care innovators treating patient populations not traditionally considered to be within the purview of primary care. Data were obtained from the 2015 Working Conference for PCMH (Patient-Centered Medical Home) Innovation funded by the Agency for Healthcare Research and Quality. The conference convened representatives from 10 innovative primary care practices and content experts to discuss experiences with integrating care for two nontraditional populations: patients with substance abuse issues and cancer survivors. Transcripts of the conference, one-on-one interviews, and written summaries of practice innovations were coded in NVivo (QSR International) and analyzed by means of an immersion/crystallization approach to identifying thematic patterns. Our study findings suggest that the politics surrounding entrenched professional identities contributed to barriers faced by conference participants in their efforts to provide innovative care for these nontraditional populations. Specifically, obstacles surfaced in relation to sharing patients across disciplinary boundaries, which resulted in issues of possessiveness, a questioning of provider qualifications, and a lack of interprofessional trust. Though support is increasing for primary care expansion and care integration, policy change may precede the identity transformations necessary for medical practitioners to embrace new primary care–centered models. For this reason, it is important that the formation and entrenchment of professional identities be critically considered as part of future efforts to transform primary care practice.