Network economics is a very hot topic, at the same time from a research point of view (with several conferences devoted to the theme, plus a devoted section in most of the other main telecommunication conferences), from a political point of view (as highlighted by the network neutrality debate, the increasing discussion on volume-based pricing, etc.), and of course from a business point of view (encompassing advertisement pricing definition, spectrum selling and sharing, bundling of offers, etc.). We believe that it is very good timing to release a book on the issue, describing both the theory and key specific applications, because of all the economic issues that constantly pop up in telecommunications. It is probably a cornerstone time for a redefinition of the Internet business model. While writing (scientific) papers on network economics, we also had the feeling that there was some room for a (new) book in the area. Indeed, there was to the best of our knowledge no recent work mixing mathematical theory and deep analysis of the economic stakes that had appeared in telecommunications. As illustrations of the issues we have in mind, we can mention the network neutrality debate, the relations between mobile network operators and mobile virtual network operators, the management of application stores, the economics of security, auctions for advertisements on different media (content pages, applications, or search engines), etc.