The POPIN Thesaurus provides alphabetical, thematic or subject, and permuted arrangements of terms. As a result of this work, the Third Edition of the POPIN Thesaurus contains approximately 100 new descriptors or terms, all of which are provided in all three languages. A total of some 240 descriptors have been deleted in order to give the thesaurus a more specific subject focus. Some 56 existing descriptors have been clarified by the addition of Scope Notes (SN) in some or all of the languages concerned. Many of the terms in all three languages have also been changed in accordance with the guidelines laid down by the POPIN Thesaurus Management Working Group, primarily to achieve closer comparability between the POPIN Thesaurus and the Macrothesaurus. A few changes in facet titles have also been made, but no major changes to the thematic organisation of the thesaurus were attempted. The POPIN Thesaurus is designed primarily for individual organisations and networks wishing to index material acquired by libraries and documentation centres and for the corresponding retrieval of such material. Second, the thesaurus may be used as a terminological guide for the standardisation of index entries such as subject headings. Third, wherever a computerized search is conducted of bibliographic databases in other subject areas, the thesaurus can be used as a search aid together with other subject-related vocabularies. Fourth, the thesaurus can be used to obtain linguistic equivalencies for translation purposes