It is argued that the structural and process models of human communication systems can be derived from the same data, and that communication systems can be described in terms of certain basic parameters; these parameters, in turn, provide a taxonomy of system types. The applicable empirical research data is reviewed to make statements about the existing knowledge concerning the structural and process facets of systems in which human beings are the components. In summary, the research literature showed that the two most commonly used models for empirical studies are the component structural model (who communicates with whom) and the component state process model (what is said after what). Matrix methods, uncertainty statistics, and graph theory methods have been employed sparingly in the analysis of communication systems data. The author concludes that communication systems, however, are organized or structured in at least three different senses, as networks of components, as sequences of components, and as sequences of component states. (RB)