A unified framework is given for multiple user information networks. These networks consist of several users communicating to one another in the presence of arbitrary interference and noise. The presence of many senders necessitates a tradeoff in the achievable information transmission rates. The goal is the characterization of the capacity region consisting of all achievable rates. The focus is on broadcast, multiple access, relay, and other channels for which the recent theory is relativdy well developed. A discussion of the Gaussian version of these channels demonstrates the concreteness of the encoding and decoding necessary to achieve optimal information flow. We also offer speculations about the form of a general theory of information flow in networks.