Educators often ask how to motivate PhD students. Before addressing how to motivate students, we should know what motivates prospective doctoral students. Motivational support has been shown to lead to overall satisfaction with the educational process, better engagement, and persistence. Using the interdisciplinary field of library and information science, this research offers insight on doctoral student motivation through quantitative analysis of results from administration of the Academic Motivation Scale. The instrument measures and classifies motivation from the perspective of self-determination theory. Results suggest PhD students are motivated by several types of intrinsic motivation as well as identified regulation, a type of extrinsic yet autonomous motivation. Findings can be used by program administrators, faculty, and other stakeholders to address the "how" of motivation through better alignment of teaching practices, research activities, and student services based on students' motivation types.