The purpose of this sequential mixed-methods study was to explore the feelings, thoughts, critical incidents, and coping mechanisms of female high school principals and their experiences with the impostor phenomenon. A hierarchical multiple regression revealed that none of the demographic factors such as number of years as a head high school principal, age, percentage of female high school principals in the district, race/ethnicity, marital status, mentorship status, and community type, were statistically significant predictors of the varying levels of the impostor phenomenon. Eighteen female principals who represented an array of backgrounds and impostor phenomenon experiences were subsequently interviewed. The interviews were evaluated using interpretative phenomenological analysis. Seven themes, including several subthemes, emerged from the data. The themes were (1) childhood socialization, including the subthemes of gender roles, familial support, and early experiences of exclusion; (2) transitional uncertainty, including hiring self-doubt, school politics, and pressure to turn around a school; (3) the principalship, including relational leadership, constant pressure, and loneliness of the position; (4) critical incidents of the impostor phenomenon, including the subthemes of lack of experience, external criticism, and self-doubt; (5) gender issues, including a male dominated position, emotional capacity, and physical appearance, (6) coping strategies for the impostor phenomenon, including mentorship and peer support, family support, and self-talk; and (7) combating the impostor phenomenon, including proven success, dismissing criticism through confidence, overcoming controversy and religion or spirituality. The results of this study suggest that mentorship, role models, familial support, and developing self-confidence can help alleviate the negative effects of the impostor phenomenon. It is recommended that educational leadership preparation programs educate students about the impostor phenomenon in an effort to normalize how they view themselves at various transitional phases of their career while offering supports to help them combat potential feelings of self-doubt that may arise as they progress through their careers. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]