The conceptual development of schema theory, the way an individual organizes knowledge, is discussed, reviewing a range of perspectives regarding schema. Schema has been defined as the interfacing of incoming information with prior knowledge, clustered in networks. These networks comprise a superordinate concept and supporting information. The information covers a wide perspective including defining features, characteristics, associations, functions, and propositions. These organizing methods allow schema to form networks with one another. Schema can be interwoven, subsumed, or enveloped by other schema. In this paper, several schema definitions are reviewed, and alternatives are presented. Applications of schema theory are illustrated, and current trends in schema research are reviewed, including the use of propositional analysis, mental models, and alternatives such as the theory of dual coding. The importance of schema theory in the development of cognitive science is discussed. One table summarizes 10 schema theories. (SLD)