When animals, including humans, communicate, they convey information and express their perceptions of the world. Because different organisms are able to produce and perceive different signals, the animal world contains a diversity of communication systems. Based on the approach laid out in the 1950s by Nobel laureate Nikolaas Tinbergen, this book looks at animal communication from the four perspectives of mechanisms, ontogeny, function, and phylogeny. The book's great strength is its broad comparative perspective, which enables the reader to appreciate the diversity of solutions to particular problems of signal design and perception. For example, although the neural circuitry underlying the production of acoustic signals is different in frogs, songbirds, bats, and humans, each involves a set of dedicated pathways designed to solve particular problems of communicative efficiency. Such comparative findings form the basis of a conceptual framework for understanding the mechanisms underlying communication systems and their evolution.