There are various views on the relationship between the interpersonal communication networks within organizations and informal social control The relative merits of some of these viewpoints can be assessed by examining the distribution of interpersonal observability in communication networks. In a study of six communication networks, it is demonstrated that there is a “horizon” to observability (a distance in a communication network beyond which persons are unlikely to be aware of the role performance of other persons). Observability tends to be restricted to persons who are either in direct contact or who have at least one contact in common. It is shown, moreover, that the number of contacts shared by two persons is a powerful predictor of the probability that one person is aware of the role performance of another, according to a simple stochastic function. Based on this evidence, some viewpoints on informal control structures are more plausible than others. A theory is presented that is consistent wi th both the present evidence and current thinking on the relationship of communication network structure and informal control. It is hoped that the theory will provide a useful starting point for future studies of this relationship.