A preliminary thesaurus of entomology covering the broad aspects of the study of insects and their relationship to man is herewith presented. The introductory material includes a short history of “word control” in entomology, the justification for a thesaurus of indexing terms in this discipline, a short history of the document itself, a description of the organization of the thesaurus, and an explanation of the use of cross-reference notations. The body of the work is divided into two main sections, one hierarchical and one alphabetical. The former, which is divided into 14 major subject-matter parts, contains about 9,000 terms with the following formalized cross references: Use (U), use for (UF), broader term (BT), narrower term (NT), related term (RT), see (SEE), see also (SEE ALSO), and scope notes (SN). It includes the Latin names of all insect and mite families likely to be used for indexing purposes. The second (alphabetized) section contains all broader and narrower terms but it employs only the USE cross reference, providing an index to the hierarchical section. Hopefully this document will provide entomologists and those in other biological disciplines, and secondary information organizations with a list of terms having authoritative application to indexing and retrieval activities in entomology.