Research on racial/ethnic categorization provides insight on how broad processes, such as migration trends or political shifts, precede the establishment of new categories, but does not detail the struggles and compromises that emerge between state and non-state actors. As a result, we know little about why new census categories are defined in certain ways or how they become legitimated. This article addresses this gap by using an organizational lens to reconstruct how the Hispanic category emerged in the United States. I demonstrate that categories can become institutionalized through a two-stage process as state actors and ethnic entrepreneurs (1) negotiate a classification’s definition and (2) work together to popularize the category. I argue that cross-field effects undergird these stages—movements toward developing a new category within state agencies are reinforced by similar classification efforts occurring among social movement groups and media firms, and vice versa. I identify three organizational mechanisms that sustained these effects in the Hispanic case: the development of boundary-spanning networks between state and non-state actors, the transposition of resources across fields, and the use of analogy and ambiguity as cognitive tools to describe and legitimate the new category. I discuss the theoretical merits of incorporating organizational analysis, especially the concept of cross-field effects, into the study of racial/ethnic classification.