AbstractThe rationale is given for creation and maintainance by an information center of a controlled indexing and retrieval vocabulary. Basic vocabulary principles are (1) use of natural language, (2) development of hospitality to new concepts, (3) provision of adequate cross‐referencing, and (4) formatting for easy use. Terminological conventions necessary for development and control of a useful vocabulary are summarized, and the techniques for applying these conventions to construct a thesaurus are described. Computerized editing techniques and updating techniques are briefly set forth.