A citation or bibliographic citation is a reference to a book, article, web page, or other published item with sufficient detail to identify the item uniquely. Unpublished writings or speech, such as working papers and personal communications, are also sometimes cited. Citations are provided in scholarly works, bibliographies, and indexes. The word citation may also mean the act of citing a work, that is, providing a reference to the work in the form of a bibliographic citation.
Citations are used in scholarly works to give credit to or acknowledge the influence of previous works, or to refer to authorities. Citations permit readers to put claims to the test by consulting earlier works. Authors often engage earlier work directly, explaining why they agree with, or differ from, earlier views. Ideally, sources are primary (first-hand) and recent.
Varying rules and practices for citations apply in scientific citation, legal citation, theological citation, prior art, patent law, and copyright law. Definitions of plagiarism, uniqueness, innovation, trustworthiness, and reliability vary so widely among these fields that the use of citations has no simple common practice.
Citations may be made in the body of text as parenthetical citations, in footnotes at the bottom of pages, or in endnotes at the end of a document. They may also be listed in a “works cited” page or section, in a bibliography, or in a list of references.
The recording, use, and reuse of citations on computers is facilitated by reference management software, also known as citation management software.
Citation indexes list published citations between various works. In addition to being used for bibliographic discovery, they are used in bibliometrics for citation analysis and the calculation of citation impact.