Traffic grooming continues to be a rich area of research in the context of WDM optical networks. Past research studies that focused on improving network utilization required high speed optical cross-connects that could switch at the packet or burst level. Such optical technologies are expensive and hard to fabricate. Recently, there have been some research into designing new architectures focused on optical grooming without using fast optical switches. Such technologies are economical, scalable, use off-the-shelf components, yet, when interconnected in a novel way provide significant network gain by aggregating traffic at the path level. In this book, a taxonomy and overview of such grooming techniques is provided. A graph theory based framework to model path level aggregation is presented. By using the model to solve the survivable design and network dimensioning problem, the trade-offs made by different architectures under different network scenarios are identified. The ideas proposed in the book will impact high speed network design and should be especially useful for network service providers, and students, professionals, and researchers working in the networking field.