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The papers in this volume consider a general area of study known as network routing. The underlying problems are conceptually simple, yet mathematically complex and challenging. How can we best route material or people from one place to another? Or, how can we best design a system (for instance locate facilities) to provide services and goods as efficiently and equitably as possible? The problems encountered in answering these questions often have an underlying combinatorial structure, for example, either we dispatch a vehicle or we do not, or we use one particular route or another. The problems also typically have an underlying network structure (a communication or transportation network). In addition, models for these problems are often very large with hundreds or thousands of constraints and variables. A companion volume in the "Handbook" series, entitled "Network Models", treats basic network models such as minimum cost flows, matching and the travelling salesman problem, as well as, several complex network topics, not directly related to routing, such as network design and network reliability.