A complete understanding of human memory will necessarily involve consideration of the active processes involved at the time of learning and of the organization and nature of representation of information in long-term memory. In addition to process and structure, it is important for theory to indicate the ways in which stimulus-driven and conceptually driven processes interact with each other in the learning situation. Not surprisingly, no existent theory provides a detailed specification of all of these factors. However, there are a number of more specific theories which are successful in illuminating some of the component structures and processes. The working memory model proposed by Baddeley and Hitch (1974) and modified subsequently has shown how the earlier theoretical construct of the short-term store should be replaced with the notion of working memory. In essence, working memory is a system which is used both to process information and to permit the transient storage of information. It comprises a number of conceptually distinct, but functionally interdependent components. So far as long-term memory is concerned, there is evidence of a number of different kinds of representation. Of particular importance is the distinction between declarative knowledge and procedural knowledge, a distinction which has received support from the study of amnesic patients. Kosslyn has argued for a distinction between literal representation and propositional representation, whereas Tulving has distinguished between episodic and semantic memories. While Tulving's distinction is perhaps the best known, there is increasing evidence that episodic and semantic memory differ primarily in content rather than in process, and so the distinction may be of less theoretical value than was originally believed.(ABSTRACT TRUNCATED AT 250 WORDS)