Empirical research on the organization of firms requires that firms be classified on the basis of their control structures. This should be done in a way that can potentially be made operational. It is easy to identify the ultimate controller of a hierarchical organization, and the literature has largely focused on this case. But many organizational structures mix hierarchy with collective choice procedures such as voting, or use circular structures under which superiors are accountable to their subordinates. I develop some analytic machinery that can be used to map the authority structures of such organizations, and show that under mild restrictions there is a well-defined ultimate control group. The results are consistent with common intuitions about the nature of control in some familiar economic settings.
