Controlling market power is a crucial issue in liberalized telecommunications market where incumbents usually remain dominant for some time after the opening of the market to competition. Controlling market power can be achieved through two distinct sets of rules and institutions: economy-wide antitrust rules and institutions, which have been in place in most industrialized countries for several decades, and infrastructure or sector-specific rules and institutions which have been specifically adopted to promote competition and control market power in telecommunications or in particular infrastructure sectors. In this context, the relationship between the two sets of rules and institutions becomes an issue of growing importance. Relying on a comparative analysis of five countries (the United States, New Zealand, the United Kingdom, Chile and Australia), the present book seeks to shed some light on how economy-wide and infrastructure or sector-specific components of the regulatory framework should be designed and on what the respective roles of such components should be to maximize the efficiency of economic regulation in telecommunications.