This paper builds a theory of organizational communication which explains communication at several system levels. The theory is built around a decision-situation model of communication theory and incorporates concepts of organization structure and behavior taken from research on complex organizations. The theory is supported with original data from five studies of organizational communication: a study of internal communication in a utility company, a study of the consumer information program of a food and general merchandise chain, a study of communication procedures of public relations practitioners in 216 organizations, a study of organization-clientele communication in a community development agency, and a study of inter-organizational communication in a community. (Author/RB)