<p>Undergraduate interprofessional education aims to prepare health professions students for a future work field characterised by wicked problems demanding interprofessional collaboration (IPC). Interprofessional identity (IPI) has been suggested as key to IPC, but how to foster its formation remains underdeveloped. Therefore, we aimed to identify (1) the main characteristics of IPI and (2) guidelines for educational design fostering interprofessional identity formation (IPIF). Per critical review methodology, we analysed educational sciences, health professions education and management sciences literature. The results of two iterative, non-exhaustive literature searches were analysed through reflexive thematic analysis. The first search focused on conceptualisations of IPI to identify its main characteristics and theories explaining IPIF, the second on the mechanisms of these theories fostering IPIF to derive guidelines for educational design. Analysis of the first search yielded five themes characterising IPI: (1) sense of belonging to an interprofessional team; (2) commitment to working interprofessionally; (3) values, attitudes, beliefs, and ethics related to IPC; (4) knowledge and understanding of roles, responsibilities, and expertise; and (5) IPC skills. We identified five prevalent theories explaining IPIF. Analysis of the second search resulted in guidelines for educational design fostering IPIF targeting the student, interprofessional team, faculty, and curriculum. Fostering IPI alongside IPC competencies is crucial for preparing students for IPC. This critical review highlighted key characteristics of IPI and proposes ED-IPIF, a theory-based framework for fostering IPIF through integrated educational design. Future research should address existing gaps and empirically test the ED-IPIF through longitudinal studies and robust tools for measuring IPI.</p>