Controlled vocabularies are a foundational concept in library science and provide a framework for consistency in cataloging practices. Subject headings provide valuable access points to library resources during search and discovery for patrons. Many librarians will be familiar with the more widely used controlled vocabularies, like those maintained by national libraries or major professional organizations. More recently, there has been an increasing shift toward specialized vocabularies maintained by independent entities intended for much narrower use. While there is valid criticism of the nature or content of controlled vocabularies, they will likely continue to be an important feature in information organization.