While interdisciplinarity has been promoted in universities for decades, research suggests that untenured faculty struggle to receive recognition for their interdisciplinary research. Informed by the microfoundations of institutional theory and discursive legitimation, we examine how members of academic departments participate in the legitimation and reproduction of tenure and promotion norms in relation to disciplinary and interdisciplinary research in a prestigious private university. Our analysis draws on 59 interviews with department chairs, directors of interdisciplinary centers, and disciplinary and interdisciplinary untenured faculty in the STEM fields, the social sciences, and the humanities. Our findings reveal three mechanisms and processes through which tenure and promotion norms become legitimated and reproduced in academic departments: 1) institutional micro-practices concerned with evaluation and gatekeeping, 2) discursive legitimation of the expulsion of interdisciplinarity at the pre-tenure stage, and 3) scholarly positioning through discursive boundary strategies directed at rationalizing the expulsion of interdisciplinarity or the expansion of existing tenure and promotion norms. Taken together, these findings advance our understanding of the tensions between the promotion of interdisciplinary research in higher education institutions, reproduction of the disciplinary order in academic departments, and interdisciplinary early-career scholars' career advancement.