This article addresses the discourse of ‘‘localism’’ used in the formulation of low-power FM radio service in the United States. It builds on S. L. Star and J. Griesemer’s (1989) concept of ‘‘boundary object’’ to theorize localism as a ‘‘discursive boundary object.’’ Drawing on interviews with advocates and regulators, participant observation with low-power radio activists, and documentary research in relevant policy discussions, the article argues that ‘‘localism’’ moved across discourse communities and effaced differences for groups who otherwise might not have agreed. ‘‘Localism’’ was also polemically deployed at the level of national policy. Its unique potency may be seen in the seeming inability of even actors who opposed the introduction of low-power FM radio service to oppose localism outright.