OBJECTIVE: To describe the professional socialization process of certified athletic trainers (ATCs) in National Collegiate Athletic Association (NCAA) Division I to guide athletic training education and professional development. DESIGN AND SETTING: We conducted a qualitative study to explore the experiences related to how participants were socialized into their professional roles in Division I. SUBJECTS: A total of 16 interviews were conducted with 11 male (68.75%) and 5 female (31.25%) participants who were either currently or formerly affiliated with an NCAA Division I athletic program. DATA ANALYSIS: The interviews were transcribed, coded, and analyzed inductively using a modified grounded theory approach. Trustworthiness was obtained by peer review, data source triangulation, and member checks. RESULTS: We identified a discernible pattern of socialization experiences and perceptions among the participants. The professional socialization processes of Division I collegiate ATCs is explained as a 5-phase developmental sequence: (1) envisioning the role, (2) formal preparation, (3) organizational entry, (4) role evolution, and (5) gaining stability. CONCLUSIONS: Examining the professional socialization process provides insights into the experiences of Division I collegiate ATCs as they prepare for their job responsibilities and develop professionally. Appropriate socialization tactics, such as the use of a structured mentoring experience, formal orientation, and staff development programming, can be implemented to promote effective professional development. Additionally, undergraduate students may be well served if they are educated to better use informal learning situations during their initial socializing events.