Vanda Broughton describes the methodology of constructing a thesaurus from a faceted classification for law (Bliss Bibliographic Classification 2nd ed. Class S). The structure of the classification is described, and the way in which the thesaural relationships are derived from this is demonstrated. Recent work to automate the process, using the encoded classification data used for the schedule display and alphabetical index, is explained. Examples of the way in which this functions are included, and an analysis of the output shows where editorial work will help to improve the resulting thesaurus.