Context: Professional socialization during formal educational preparation can help students learn professional roles and can lead to improved organizational socialization as students emerge as members of the occupation's culture. Professional socialization research in athletic training is limited.Objective: To present the role of legitimation and how it influences the professional socialization of second-year athletic training students.Design: Modified constructivist grounded theory and case study methods were used for this qualitative study.Setting: An accredited undergraduate athletic training education program.Patients or Other Participants: Twelve second-year students were selected purposively. The primary sample group (n 5 4) was selected according to theoretical sampling guidelines. The remaining students made up the cohort sample (n 5 8). Theoretically relevant data were gathered from 14 clinical instructors to clarify emergent student data.Data Collection and Analysis: Data collection included document examination, observations, and interviews during 1 academic semester. Data were collected and analyzed through constant comparative analysis. Data triangulation, member checking, and peer-review strategies were used to ensure trustworthiness.Results: Legitimation from various socializing agents initiated professional socialization. Students viewed trust and team membership as rewards for role fulfillment.Conclusions: My findings are consistent with the socialization literature that shows how learning a social or professional role, using rewards to facilitate role performance, and building trusting relationships with socializing agents are important aspects of legitimation and, ultimately, professional socialization.Key Words: clinical education, preservice professional preparation, socializing agents, role performance, grounded theory Key Points N Athletic training education should incorporate effective socialization strategies to improve the quality of clinical educational experiences for athletic training students and promote their legitimation as developing athletic trainers.N Successful role performance is an important determinant of legitimation and professional socialization of preservice athletic trainers. Efforts should be made programmatically to orient students to program goals and expectations and to decrease potential role conflict, which could be a negative effect of insufficient socialization.N Developing relationships facilitates legitimation in preservice athletic trainers. Thus, individuals such as patients, coaches, clinical instructors, and peer mentors serve as socializing agents to preservice athletic trainers and should be considered when developing socialization strategies for preservice and inservice professionals.