This book presents the history and state of the art of universal routing strategies, which can be applied to networks independently of their respective topologies. It opens with a self-contained introduction, accessible also to newcomers. The main original results are new universal network prools for store-and-forward and wormhole routing with small buffers or without buffers; these results are presented in detail and their potential applications are discussed. The book ends with a summary of open problems and an outlook of future directions in the area of routing theory.