The radio-frequency spectrum is the part of the natural spectrum of electromagnetic radiation lying between the frequency of 3 kilohertz (kHz) and 300 gigahertz (GHz). It is the medium that makes possible wireless communications and supports a vast array of commercial and governmental services. Commercial entities use spectrum to provide a variety of wireless services, including mobile voice and data, paging, broadcast television and radio, and satellite services. Federal, state, and local agencies use spectrum to fulfill a variety of government missions, such as national defense, air-traffic control, weather forecasting, and public safety. Spectrum is managed at the international and national levels. The International Telecommunication Union (ITU), a specialized agency of the United Nations, coordinates spectrum management decisions among nations. Spectrum management decisions generally require international coordination, since radio waves can cross national borders. Once spectrum management decisions are made at the ITU, regulators within each nation, to varying degrees, follow the ITU decisions. In the United States, responsibility for spectrum management is divided between two agencies: FCC and the Department of Commerce’s National Telecommunications and Information Administration (NTIA). FCC manages spectrum use for nonfederal users, including commercial, private, and state and local government users under authority provided in the Communications Act. NTIA manages spectrum for federal government users and acts for the President with respect to spectrum management issues. FCC and NTIA, with direction from Congress and the President, jointly determine the amount of spectrum allocated to federal and nonfederal users, including the amount allocated to shared use. Historically, concern about interference or crowding among users has been a driving force in the management of spectrum. FCC and NTIA work to minimize interference through two primary spectrum management functions—the “allocation” and the “assignment” of radio spectrum. Specifically:  Allocation involves segmenting the radio spectrum into bands of frequencies that are designated for use by particular types of radio services or classes of users. For example, the frequency bands from 88 to 108 MHz are allocated to FM radio broadcasting in the United States. (Fig. 1 illustrates examples of services by frequency band.) In addition to allocation, spectrum managers specify service rules, which include the technical and operating characteristics of equipment.  Assignment, which occurs after spectrum has been allocated for particular types of services or classes of users, involves providing users, such as commercial entities or government agencies, with a license or authorization to use a specific portion of spectrum. For example, FCC assigned a license for the 88.5 MHz band in Washington, D.C., to American University, for its radio station, WAMU. FCC assigns licenses for frequency bands to commercial enterprises, state and local governments, and other entities, while NTIA makes frequency assignments to federal agencies. In some frequency bands, FCC authorizes unlicensed use of spectrum— that is, users do not need to obtain a license to use the spectrum. Rather, an unlimited number of unlicensed users can share frequencies on a noninterference basis. Thus, the assignment process does not apply to the use of unlicensed spectrum. However, manufacturers of unlicensed equipment must receive authorization from FCC before operating or marketing an unlicensed device. Traditional unlicensed equipment consists of low-powered devices that operate in a limited geographic range, such as cordless phones, baby monitors, garage door openers, and wireless access to the Internet. When FCC assigns a portion of spectrum to a single entity, the license is considered exclusive. When two or more entities apply for the same exclusive license, FCC classifies these as mutually exclusive applications—that is, the grant of a license to one entity would preclude the grant to one or more other entities. Since 1994, FCC has primarily used auctions to assign spectrum for mutually exclusive applications. Auctions are a market-based mechanism in which FCC assigns a license to the entity that submits the highest bid for specific bands of spectrum. FCC was provided with authority to use auctions to assign mutually exclusive licenses for certain subscriber-based wireless services in the Omnibus Budget Reconciliation Act of 1993. FCC implemented its auction authority conducting its first auction in 1994. In subsequent years, Congress has modified and extended FCC’s auction authority, including exempting some licenses from competitive bidding, such as licenses for public safety radio services and noncommercial educational broadcast services. FCC’s auction authority is scheduled to expire on September 30, 2012. As of June 30, 2011, FCC had conducted 79 auctions to select between competing applications for the same license, which have generated nearly $52 billion for the U.S. Treasury. However, only about 3 percent of licenses have been auctioned. The vast majority of the other 97 percent of licenses were assigned through other means before FCC began using auctions. In March 2010, an FCC task force issued the National Broadband Plan. Because broadband access and use is becoming increasingly wireless, the plan includes a set of recommendations aimed at ensuring efficient allocation and use of radio-frequency spectrum for wireless broadband services. The plan recommended that FCC make 300 MHz of spectrum newly available for mobile broadband use in the next 5 years and 500 MHz of spectrum for broadband within the next 10 years. In June 2010, the President issued a memorandum with a similar goal for NTIA working in collaboration with FCC. To accommodate new commercial uses of spectrum, such as wireless broadband, FCC must often change its rules to move certain bands of spectrum from an existing use to the new use, a process known as repurposing spectrum. However, this process can be lengthy—from 7 to 15 years for the six repurposings that we examined. We identified the following factors that contribute to the time it takes FCC to repurpose spectrum: the regulatory nature of repurposing, opposition of incumbent users, FCC and NTIA coordination on the repurposing of federal spectrum, and concerns about interference. FCC identified voluntary approaches that it thinks could speed the process by, for example, avoiding some opposition; however, these approaches generally require congressional approval and face some stakeholder opposition. Since most of the usable spectrum in the United States has been allocated to existing uses, FCC must often repurpose spectrum from an existing use to make it available for new uses. When there are competing interests for specific spectrum, FCC determines which use or uses of the spectrum will best serve the public interest, considering factors such as economic and social value, including importance for public safety. FCC also seeks to ensure that the spectrum is technically suitable for the new use. To repurpose spectrum for a new use, FCC uses a three-phase process: Identification. As a first step, FCC identifies a spectrum band, or bands, that appear to be good candidates for repurposing. To identify candidate bands, FCC conducts a formal study or releases a notice of proposed rulemaking soliciting industry input, or another party, such as NTIA or Congress, identifies a candidate band.  Reallocation. FCC subsequently reallocates the spectrum by changing the designated use of the spectrum. FCC develops service and other technical rules for the spectrum that define (1) the eligibility criteria for users, (2) the services that users can provide, (3) the time frames and other requirements for users to build the infrastructure required to support the services, and (4) the interference limits.  Reassignment or secondary markets. If the new use entails a licensed use of the spectrum, new users must be assigned, or provided authorization, to use the spectrum. In some cases, FCC reassigns the spectrum to new entities, often using auctions. In other cases, FCC permits incumbent licensees to sell or lease their licenses to other entities, through a process known as secondary market transactions. If the new use entails an unlicensed use of the spectrum, FCC does not need to complete a reassignment. Since 1994, FCC has completed six major repurposings of spectrum, which have made over 520 MHz of spectrum available for new commercial uses. In most instances, FCC repurposed the spectrum to enable mobile broadband service. Five of the six repurposings collectively generated over $47 billion in auction revenues, which provides one measure of the new economic value arising from the repurposing. The former uses of the repurposed spectrum included microwave services, specialized mobile radio services (such as those used in radio dispatch systems), and one-way systems that transmit video (see table 1). The six major repurposings we reviewed took from 7 to 15 years to complete, from the identification through the reassignment phase. For example, the Enhanced Specialized Mobile Radio repurposing took 7 years while three repurposings—Personal Communications Service, Advanced Wireless Services-1, and 700 MHz Wireless—took over 10 years to complete (see fig. 2). Similar to our findings, in the National Broadband Plan, FCC noted that the process of revisiting or revising spectrum allocations has historically taken 6 to 13 years. In addition to the time required to complete the repurposing process (identification through reassignment), time is needed to relocate existing users and allow new users to construct new wireless networks before new services can be made available using the repurposed spectrum. Typically, existing users must relocate to a new spectrum band or bands, and new users must construct the infrastructure required to support their services. While the participants undertake most of these actions, FCC and other government agencies’ actions and decisions can influence the time frames. For example, FCC held the first auction for the Advanced Wireless Services-1 repurposing in 2006, but NTIA expects that it will take until 2013 for all federal agencies to relocate from the spectrum that was repurposed for commercial use. In addition, FCC allowed licensees 15 years from the inception of their license term to begin providing substantial service.