The Australian Pictorial Thesaurus (APT) is a hierarchical thesaurus of over 15,000 Australian subject terms for the indexing of images and other original material collections. It provides a common indexing language for describing pictorial and other collections of Australian libraries, archives and museums. It is an authoritative vocabulary, compiled and maintained on established principles of thesaurus construction. The APT uses contemporary Australian words and phrases to describe objects, people, places, activities and concepts. The range and depth of APT terms facilitate the precise indexing of images and collections. Using APT terms will facilitate subject searches across national collections. Terms idiomatic to a particular state are not included, so users requiring such terms should contact their own state library for advice.