The impostor phenomenon (IP) is characterized by denial of competence and discounting achievements combined with a fear of failure and fear and guilt about success (Clance & Imes, 1978). People with impostor feelings engage in behaviors such as perfectionism, which may lead to accolades, yet paradoxically hinder subsequent achievements. The purpose of this dissertation was to explore how graduate student women describe their experiences of IP and to investigate how IP affects their careers. The mixed-method design incorporated data from two focus groups, 506 survey responses, and eight interviews. Nearly 3 in 4 women self-identified with IP, however, it emerged in different ways (e.g., fear of making mistakes, second-guessing merits, attributing success to flukes). Findings showed that impostor feelings were associated with psychological constructs (i.e., perfectionism, core self-evaluations, and symptoms of anxiety and depression) in hypothesized directions. Women described multiple ways their salient identities compounded impostor feelings. Regarding career- related consequences, women often inhibited themselves by not submitting applications, staying silent, not venturing outside their comfort zone, isolating, procrastinating, setting lower goals, or quitting. Results also uncovered poor psychometric properties of the widely used Clance Impostor Phenomenon Scale, therefore, caution is encouraged when using this scale in the future. This indicates a need for clearer construct definition and measurement, potentially with two new scales generated from this study. Women shared hundreds of suggestions such as a shift in mindset in terms of attitude regarding schooling, expectations, and taking ownership of achievements. Additionally, sharing impostor feelings with others emerged as an overarching theme. Overall, findings point to the urgency of clarifying the construct and future replication studies with other populations and methods, particularly given the proliferation of writing about "imposter syndrome." Results may inform modifications to graduate training programs and interventions to promote women's career development during their time in graduate school and in their subsequent 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.]