This book focuses on methods for service-differentiated and constraint-based wavelength routing and resource allocation for multi-service WDM networks, tailored at needs of specific network users and adaptable to services yet to emerge. A number of unique routing solutions are proposed, and an extensive analysis of dynamically re-configurable multi-service WDM networks impart the major contribution to the current efforts in standardisation and network operation, and give an inimitable motivation for further study and research.