This paper analyzes how organizations can minimize costs of processing and communicating information. Communication is costly because it takes time for an agent to absorb new information sent by others. Agents can reduce this time by specializingin the processing ofparticular types ofinformation. When these returns to specialization outweigh costsofcommunication, it is efficient for several agents to collaborate within a firm. It is shown that efficient networks involve centralization, that individuals delegate tasks to subordinates only if they are overloaded, and that the number of transits to the top tends to be equalized across individual information items.