Corporate mergers and the consolidation of ownership in the American communications arena have long been sources of concern. US regulatory and antitrust policy traditionally attempted to secure a "diversity of voices" structurally, largely through rules regarding ownership. Although the meaning of diversity was always problematic and under-theorized, the Federal Communications Commission long set ceilings on the numbers of broadcast outlets any single person or corporation could own and enacted cross-ownership rules such as a prohibition against a corporation owning a newspaper and broadcast outlets in the same market. These rules, and the FCC's authority to make them, were upheld, occasionally even compelled, by the federal appellate courts. In the last 20 years, however, legal trends, in conjunction with political developments, have undermined the diversity rationales behind ownership rules and associated structural regulations of mass media.Paradoxically, even as media corporations are becoming larger and presumably more powerful, ownership regulations are being rescinded or struck down. This paper explains this history. It concludes with a suggestion that the First Amendment metaphor of marketplace of ideas is misplaced and how our thinking about media ownership and diversity might be better served by the metaphor of a mixed media system.