Context: Advanced clinical practice is inherent in contemporary athletic training education, such as residency programs and Doctor of Athletic Training programs; however, as a concept, advanced clinical practice in athletic training has been poorly studied to date. Objective: To explore athletic trainers' perceptions of advanced clinical practice. Design: Cross-sectional. Setting: Online survey with open-ended questions. Patients or Other Participants: Three hundred fifty of 1992 athletic trainers accessed the survey (17.6% access rate); 321 respondents completed at least 1 open-ended question; and 196 completed the survey in its entirety (61.1% completion rate). Intervention(s): We used a 13-item survey including demographic items (9 items) and open-ended response questions (4 items). Main Outcome Measure(s): Guided by the consensual qualitative research approach, a 3-person data analysis team coded the open-ended responses. Each member coded 50 responses and a consensus codebook was developed. Two members of the team coded the remaining responses, which were confirmed by the third member. Emergent data were organized into themes and categories, and frequency counts were determined for each category. Results: Athletic trainers' definitions of advanced clinical practice were categorized into 4 emergent categories: (1) formal training and education; (2) informal training and education; (3) knowledge, skills, and behaviors; and (4) experience and uncertainty. Conclusions: The categories of formal and informal training and education focused on athletic trainers acquiring additional knowledge and skills through mechanisms such as postprofessional degree programs, residency programs, or other areas of study. The knowledge, skills, and behaviors category included areas related to specialized skills and the core competencies. These 3 categories aligned with one another to provide both the types of knowledge, skills, and behaviors that define advanced clinical practice, and the specific mechanisms through which an athletic trainer can achieve advanced clinical practice.