INTRODUCTION Unless a researcher is already completely familiar with all books and articles in a particular subject (and who is?), it is necessary to do subject searches. Finding material on a particular subject is often more complicated than it seems. However, whether searchers are looking for books or articles, and whether they are looking in a paper card catalog or index, or in a computer public terminal or database, some basics stay the same. Using the right terms to look up a subject is one of the most critical steps in ﬁnding useful material, along with looking in the right places. Naturally, there are many aids to help researchers ﬁnd the material they are looking for. The vocabulary used by the people who classify books and create article indexes is one important aid.