This paper is concerned with organizational information systems. Examples of such systems include intelligence systems, communications systems, management information systems, decision support systems, and administrative control systems. Systems such as these are critical to an organization's functioning; indeed to its survival. The paper is intended to be of use to three types of professionals: those who study organizations; those who design information systems; and those who manage. This fact causes the paper to differ in a number of ways from earlier works dealing with organizational communications and related topics. For example, the paper draws on three different literatures: the psychological literature dealing with perception and cognition, the social-psychological literature dealing with the role of motivation in communications, and the organizational literature dealing with behavior in information systems. Further, the paper gives greater attention than do earlier works to logistical determinants of information system effectiveness, such as the workload of the unit processing the message or the priority assigned to a message, as contrasted with social-psychological determinants. Finally, the explicit introduction of judgment and argument by analogy when direct evidence is unavailable is a third way in which the paper differs from earlier works. The paper focuses in particular on the determinants of the performance and behavior of systems such as those mentioned above. It discusses in some detail the impact of these determinants on four processes that are of key importance in the operation of information systems. Two of these processes are used to increase system efficiency. One, message routing causes any particular message to be distributed to relatively few organizational units, and thus greatly reduces the information processing load of the many units that might otherwise be involved in receiving or relaying the message. The other, message summarizing, plays a similar role. It has as its purpose reducing the size of the message while at the same time faithfully reproducing its meaning. The remaining two processes follow from the fact that organizational units necessarily exercise some discretion in the way that they handle messages. Message delay is a consequence of the priority assignment given a message, and in many cases enhances the effectiveness not only of the operating unit but of the organization as a whole. Message modification refers to the distortion of message meaning. Its source may be either the cognitive limitations or the motivations of the sender or receiver. Modifications may be conscious or unconscious, well-intended or malicious. Each of these four processes is discussed in some depth. More specifically, the several determinants of the probability or extensiveness of each process's occurrence are identified. The literature related to the various process-determinant pairings is then reviewed, and is summarized in the form of propositions. Several areas where additional research is needed are noted and recommendations are made concerning what the nature of such research should be.