Cooperative Communications reviews progress in cooperative communication networks. It assembles a representative sample of recent results to serve as a roadmap for the area. The emphasis is on wireless networks, but many of the results apply to cooperation in wireline networks and mixed wireless/wireline networks. Cooperative Communications is intended as a tutorial for the reader who is familiar with information theory concepts but has not actively followed the field. For the active researcher, it serves as an invaluable digest of significant results. It is designed to encourage readers to find new ways to apply the fundamental ideas of network cooperation. It is also intended to make the area sufficiently accessible to practicing network designers.