This book provides a broad overview of IP over WDM technologies, as seen by a group of experts participating in the e-Photon/ONeC and BONE Networks of Excellence funded within the VIth and VIIth Research Framework Programmes (FP6 and FP7) of the European Union. Both Networks of Excellence are aimed at the integration of research teams active on optical networks at a pan-European level, with the creation of virtual centers of excellence in optical networks, te- nologies, and services. The working groups on optical core networks gathered about a 100 researchers from more than 20 universities and research institutions in Europe. The multifaceted viewpoints available in this community on the current state and future evolution of large WDM networking infrastructures are reported in this book. The book is organized in chapters, with chapter editors, listed on pp–, having the responsibility to collect and harmonize contributions by different - search groups. The whole work was made possible by the coordination efforts of Javier Aracil and Franco Callegati, leaders, at the time when the book writing was begun, of the working groups on optical core networks and on optical burst swit- ing in e-Photon/ONeC. We are thankful to them for their efforts. We hope that this manuscript will serve as a valuable reference for students and practitioners in the ?eld of optical networking.