This book begins with an introduction into the interested area and a description of the basic mechanisms behind Programmable Router routes. Examination of existing Programmable Router systems and associated technologies is provided. The core of the book presents the design and implementation of a novel Programmable Router architecture that enables flexible network programmability based on so-called "user components". This Programmable Router is designed to provide maximum flexibility for the development of future network functionality and services. Its service composition method enables flexible programmability through the transparent integration of user components into the router¿s data path. Finally, the success of the node architecture and its prototype implementation is evaluated by means of a few concrete applications. This shows that the Programmable Router offers sufficient flexibility and extensibility to augment the network in ways that suit today¿s fast evolving internetwork platform, and the prototype implementation confirms that the research platform offers acceptable performance for edge-routers of small-to-medium sized network environments.