Legitimacy is widely invoked as a condition, cause, and outcome of other social phenomena, yet measuring legitimacy is a persistent challenge. I synthesize approaches to conceptualizing legitimacy across the social sciences to identify widely agreed upon definitional properties, and build on these points of consensus to develop a generalizable approach to operationalization. Legitimacy implies specific relationships among three empirical elements: an object of legitimacy, an audience that confers legitimacy, and a relationship between the two that is defined by mutual expectations. Together, these empirical elements constitute a dyad (i.e., a single unit consisting of two nodes and a tie). By accounting for the ways that elements of the dyad interact, legitimacy (and illegitimacy) can be empirically established. I outline how this operationalization is compatible with approaches to theorizing legitimacy found in areas of study ranging from small group processes to institutional analysis. Followed to its logical conclusion, this operationalization has important implications for the study and theorization of legitimacy. It implies that legitimacy operates in the context of dyads, and does not function as an attribute of individuals, organizations, regimes, or other social objects. Consequently, the effects of legitimacy are limited to interaction between object and audience in the dyad. Finally, both the establishment and effects of legitimacy are mediated by network dynamics.