This book presents a comprehensive view of Internet intermediaries, their economic and social function, development and prospects, benefits and costs, and roles and responsibilities. Divided into three parts, Part I, The Economic and Social Role of Internet Intermediaries, develops a common definition and understanding of what Internet intermediaries are, of their economic function and economic models, of recent market developments, and discusses the economic and social uses that these actors satisfy. Part II, The Role of Internet Intermediaries in Advancing Public Policy Objectives, examines the roles and responsibilities of Internet intermediaries in advancing public policy objectives, as well as the costs and benefits of their involvement through a series of case studies. Part III provides a summary of an experts workshop that identified lessons learned and best practices from the experience to date of Internet intermediaries in advancing public policy objectives.