The activities of commercial wireless companies in the United States before World War I were critical forerunners of the unique system of property rights in the radio spectrum that developed in the United States between 1899 and 1927. These activities formed the basis for commercial claims to property rights in the spectrum during the 1920s, when radio broadcasting developed. The early wireless companies provided the material, institutional, and ideological foundations for commercial rights in the spectrum that are still a striking part of mass communication in the United States today. The De Forest/United Wireless succession of companies, although ultimately business failures, nonetheless laid the groundwork for commercial radio in the United States. Most historians of radio have overlooked the importance of the pre–World War I period, and all have neglected the contribution of the De Forest/United Wireless companies.