twork theory pays attention to the nodes and links that form networks. The architecture of networks affects transmission capacity and the quality of service. The structure of networks also is important for understanding the boundaries of private networks provided by individual firms and the intercon- nections between networks. By applying network theory to communications, we develop a general Coasian theory of networks. Using network theory, we develop a comprehensive framework for analyzing public policy toward communications. The discussion identifies the shift in regu- latory policy from utility regulation to mandated access. Access to networks refers to the market transactions that connect a firm's network to its customers, suppli- ers, competitors, and partners. Our discussion presents a classification scheme for analyzing access to networks. We apply network theory based on the mathemat- ics of graph theory tools to characterize the structure of networks. We examine how regulatory access mandates can distort access price. In competitive markets, optimization by firms and access transactions lead to efficient network boundaries and interconnections. Regulatory access mandates potentially reduce economic efficiency by changing the market-equilibrium structure and boundaries of com- munications networks. A. The Changing Network Economy Economic growth in the modern economy has accompanied a dramatic upsurge in the importance of communications networks. Consumers and businesses have Networks in Telecommunications become linked together with ever-faster connections transmitting a growing amount of data for electronic commerce, organizational management, and social interaction. Communications networks have joined more traditional network industries in energy and transportation in playing a pivotal role in the func- tioning of national economies. The information and communications technol- ogy (ICT) industries form a growing share of the global economy (U.S. Depart- ment of Commerce 2003). International trade has 