This document discusses controlled vocabularies, which are organized lists of words and phrases used to tag and categorize content. Controlled vocabularies help impose order on terminology to facilitate searching and browsing. They include thesauri, subject headings, and ontologies. An example is given of how a retailer like GAP would use a controlled vocabulary hierarchy to organize the many types of pants they sell. The benefits of controlled vocabularies include improved searching, navigation, and personalization, while the challenges include the work required to create and maintain them. The process of creating a controlled vocabulary involves determining concepts, selecting terms, and applying general principles like specificity and direct entry.