ln environments with private information and spatial separation, the ability of agents to establish mutually beneficial arrangements can be limited by their ability to communicate contemporary dealings and histories of past dealings. Indeed, with the extension of some recent work in contract theory and mechanism design, this paper argues that location or person-specific assignment systems, portable object record-keeping systems, written message systems, and telecommunication systems can be viewed as communication systems which are successively more complete in this sense. An attempt is made also to match these various communication systems with systems in use in historical primitive, and/or contemporary societies and to interpret these communication systems as financial structures.