This thesaurus was developed as a guide for the indexer and has been published to aid the users of the information services provided by the Radiation Chemistry Data Center. The indexing terms listed in the thesaurus are those found in the RCDC Bibliographic Data Base and therefore are the terms used to generate the keyword index in this volume. The RCDC thesaurus covers radiation chemistry in depth, as well as related topics in phtochemistry, luminescence, esr and the kinetics of reactive intermediates. New terms are added as needed, necessitating successive revision of the thesaurus.