PURPOSE: To unravel boundary crossing as it relates to professional identity formation in pharmacists transitioning from a community pharmacy to working as nondispensing clinical pharmacists in general practice, with the aim of optimizing their education. METHOD: This was a multiple-case study, including two-stage interviews, peer feedback, and individual reflection, that collected data in 2014-2016 from eight clinical pharmacists working in general practice in the Netherlands. These pharmacists acted-without a workplace role model-as pharmaceutical care providers in general practices during a 15-month training program. In within-case and cross-case analysis, data were collected regarding pharmacists' role development in practice and perceptions of learning processes, and examined through the lens of professional identity formation and boundary crossing. RESULTS: Analysis of data collected during and after the training program demonstrated that the clinical pharmacists who applied the learning mechanisms of reflection and transformation developed a patient-care-oriented professional identity. Some clinical pharmacists, who learned mainly through the mechanism of identification, did not integrate the new patient-care-oriented role into their professional identity. They felt that their workplace provided limited opportunities for reflection and transformation. Learning with peers on formal training days was seen as highly valuable for professional identity formation; it counterbalanced the lack of a role model in the workplace. CONCLUSIONS: Professional identity formation in the transition from community pharmacist to clinical pharmacist in general practice benefited from reflective, on-the-job training. This permitted transformative, boundary-crossing learning with peers and supported professional identity formation oriented to providing practice-based pharmaceutical care.