Book excerpt: Most animal communication has evolved and now takes place in the context of a communication network, i.e. several signallers and receivers within communication range of each other. This idea follows naturally from the observation that many signals travel further than the average spacing between animals. This is self evidently true for long-range signals, but at a high density the same is true for short-range signals (e.g. begging calls of nestling birds). This book provides a current summary of research on communication networks and appraises future prospects. It combines information from studies of several taxonomic groups (insects to people via fiddler crabs, fish, frogs, birds and mammals) and several signalling modalities (visual, acoustic and chemical signals). It also specifically addresses the many areas of interface between communication networks and other disciplines (from the evolution of human charitable behaviour to the psychophysics of signal perception, via social behaviour, physiology and mathematical models).