Disciplinary identity, or connection to a particular academic discipline, is constructed through a developmental process across a scholar's academic life course. Using unique data from an online survey of students at four different colleges and universities, we investigate the extent to which disciplinary identity among undergraduate researchers reflects motivations for participating in research and varies by student discipline. We document key differences in disciplinary identity based upon two internal motivators, intellectual interest and grit, as well as demographic characteristics. We discuss implications for institutions and undergraduate programs desiring to encourage students to participate in undergraduate research.