This new edition has the same purpose as its predecessors; i.e., to provide language which can process information relating to all aspects of economic and social development, and, at the same time, give a common dimension to the more specific vocabularies corresponding to each of them. However, it differs from previous editions on five major counts: structure, field coverage, choice of national languages, number and form of descriptors, and printing. The structure provides alphabetical, descriptor group, and hierarchical displays, and a KWOC index including scope notes, broader, narrower, and related terms, and synonyms. The fields of study are further developed in such areas as population, health, environment, cultural development, communication, education, and energy conservation. The three languages used are those considered as the most significant and widely used in the development of literature: English, French, and Spanish; German has been dropped. The number of descriptors has doubled, despite removal of obsolete and irrelevant terms. Precoordination is used for precision where necessary, plurals are preferred to singulars, related terms are increased, the hierarchy has been improved, and scope notes have been revised to reduce ambiguity. Capital letters are used throughout in heavier and lighter print to increase readability. (RAA)