Threshold concepts have been widely utilized to understand learning in academic disciplines and student experiences in a disciplinary curriculum. This study considered how threshold concepts might operate within an interdisciplinary setting. Data were collected through interviews with 40 doctoral students enrolled in an interdisciplinary program as well as content analysis of interdisciplinary curricula. The findings emphasize the importance of the integrative process to interdisciplinary initiatives. Interdisciplinary threshold concepts do not result from the addition of multiple disciplines, but rather are fostered through unique facets of the interdisciplinary experience.