Objective – To examine how an academic librarian’s years of instructional experience impacts how they think of themselves as instructors. Design – Survey questionnaire. Setting – American academic library profession. Subjects – 353 participants selected from 501 respondents. Methods – A Qualtrics survey was sent via email to members of several American Library Association discussion lists. The author selected a subset of respondents for further analysis based on how they answered key questions on the survey. Selected participants were those who believed they had experienced perspective transformation around their teaching identities. The author used principal component analysis and confirmatory factor analysis to identify twelve transformative constructs across three sub-themes: relational, experiential, and professional inputs. The author then labelled each construct based on its respective component parts. One-way analysis of variance (ANOVA) tests were then conducted using SPSS. Main Results – Statistically significant differences were found between experienced and inexperienced instructional librarians. Participants with more instructional experience tend to believe their teaching identities are influenced to a greater extent by these factors: • Interpersonal relationships • Feedback from colleagues outside of librarianship • Self-directed learning opportunities Participants with less instructional experience tend to believe their teaching identities are influenced to a greater extent by these factors: • Feedback from those within librarianship • Library-centric inputs such as their formal library studies Conclusion – Different types of professional development opportunities will appeal to different librarians based on their level of instructional experience. Less experienced librarian instructors may find mentoring and informal collegial relationships within the library to be beneficial. More experienced librarian instructors may prefer to seek out relationships with colleagues outside the library to further develop their teaching identities.