Authority control is the means by which catalogers maintain consistency of form, or a controlled vocabulary, in catalog headings (names, places, titles, subjects). This optimizes retrieval by enabling users to find all works associated with a particular name, title, or topic under a single, authoritative form of the name, regardless of which variant the user searches under. For example, the authorized subject heading for works about cars is "Automobiles," and all items about that topic will be assigned that heading, including a film entitled All About Cars. A cross reference is made from the term "Cars" to the heading "Automobiles" to ensure that anyone looking under "Cars" will be pointed to the correct heading (or directly to the records under that heading).
Authority work is the process of determining and recording the authoritative form of a heading, its variants and related terms, and documenting the decision-making process. The end product of this work is the authority record, which indicates the authorized form of the heading, see and see also references, and the cataloged work which generated the heading. It may also list other authoritative sources consulted and provide scope notes to define the term, distinguish it from other similar terms, and instruct as to application. Although an authority record may be very simple or very detailed, it essentially consists of three parts: the authoritative form of term (heading), cross references if any, and notes if applicable.
Without authority control works by or about a person or other entity would be scattered in the file. For example, Edward, Duke of Windsor might be found under Edward, or under Duke of Windsor, or Prince of Wales, or Prince Edward, or Edward VIII. A user should be able to search under any of these variants of "Edward" and retrieve all works by or about this person. The authority record indicates the authorized form of name, in this case, Windsor, Edward, Duke of, 1894-1972, and lists all the variants as cross references.
Conversely, authority control allows users to distinguish between two people with the same name. For example, there are a number of queens named Elizabeth: Queen Elizabeth II, her mother (Elizabeth, Queen and consort of George VI), and several other contemporary queens of that name from Luxembourg, Yugoslavia, Romania, Greece, and Belgium, to cite a few. Similarly, authority control allows users to distinguish between two different subjects known by the same term, e.g., Casting (fishing) and Casting (founding).
Ideally, authority records should be linked to bibliographic records (the descriptions) so that a user can search on a variant heading and retrieve all records containing the authorized form of the heading.