In contrast to existing theories of organizations that stress the vertical control of intraorganizational interaction, a structural perspective is discussed that emphasizes the networks of social interaction that develop horizontally and diagonally, as well as vertically, across the organization. As an example of this perspective, the effects of the hierarchical arrangement of positions, both in terms of the unequal number of individuals in vertical levels and in terms of the differential allocation of resources across vertical levels, is hypothesized to lead to differential rates of interaction across the organization. These effects of structural differentiation on networks of interaction are tested in a public bureaucracy, and the implications of differentiation for the formation of networks of interaction and resulting collective actions such as coalition formation are discussed.