This report summarizes the work carried out on the automatic construction of keyword classifications and their use in information retrieval. It discusses the possible characteristics of such classifications, and potential ways of using them; and describes the various approaches to classification that were considered in terms of an overall frame of reference in which several types of classification are distinguished. The result of experiments using a collection of documents and test requests obtained from the Aslib Cranfield project are presented, from which it can be concluded that automatic classifications, which lead to noticeable improvements in retrieval performance over those obtainable with unclassified terms, can be set up. (Author/AB)