Cite sources (citation): provide references that help the reader to check the veracity of the article and to find more information. Good citations are critical to help make Wikipedia trusted and useful.

If you consult an external source while writing an article, citing it is basic intellectual honesty. More than that, you should actively search for authoritative references to cite. If you are writing from your own knowledge, then you should know enough to identify good references that the reader can consult on the subject—you won't be around forever to answer questions. (Also, this forces you to check your facts, and you might find that you don't know everything.) The main point is to help the reader—cite whatever you think will be most helpful.

This applies when writing about opinions, as well—beware the temptation to write weasel phrases like, "Some people say..." Who said it, and where and when? (Remember that Wikipedia is not for your opinions or for original research.)

This applies even when the information is currently undisputed — even if there's no dispute right now, someone might come along in five years and want to dispute, verify, or learn more about a topic. For disputed claims, it's extremely helpful to have a citation so that the issue can either be investigated (by readers) or resolved (by the Wikipedia editing community).

Adding citations to external sources, especially for information in articles not already backed by citations, is also a good way to enhance even articles you didn't write.

References should typically be collected at the end of the article under a ==References== heading; see below for a proposed style. The most important thing is to enter the complete reference information, however; details like formatting can be dealt with later if necessary, but it's sometimes difficult for others to track down your sources. You can quickly insert inline references to web pages by inserting a URL surrounded by single square brackets; this doesn't provide as much information to readers, but it's much better than not citing your sources at all. For example, to cite the present page this way, you would insert [http://en.wikipedia.org/wiki/Wikipedia:Cite_sources], which the reader would see as [1] (http://en.wikipedia.org/wiki/Wikipedia:Cite_sources).

Citations in the text and at the end

At the end of an article, under a ==References== heading, list the complete reference information as a bulleted (*) list, one per reference work. (A numbered reference list, although common in many publications, is currently discouraged in Wikipedia; see below for discussion of this.)

In addition to listing a reference at the end, you may choose to embed a pointer to a particular reference within the article text. To do this, cite references parenthetically as "(Author-Last-Name, Year)". Use the original publication year for a re-published work. If the cited information is not easy to find with just that information (for example, it's a poorly indexed topic in a large book), add chapters ("chap. 3") or pages ("p. 15" or "pp. 12–23") after the year (separating the two with a comma). When a reference is used as a noun, put the year in parentheses, e.g. "Milton (1653) says..." For two authors, use (Author1 & Author2, year); for more authors, use (Author1 et al., Year).

If there are few references and the material is uncontroversial, in-text citations are often unnecessary. However, in-text references can be very useful if there is a long list of references and it is not clear which one the reader should consult for more information on a specific topic. In-text citations can also be extremely useful if there is doubt or disagreement on some point; the text can claim that a report stated something, and then you can reference that report. In particular, articles that involve strong opposing viewpoints may need to have many in-text citations to justify many of their statements.

An example citation style

Formatting of the reference list is a secondary detail, and there is currently no consensus on a precise prescribed citation format in Wikipedia. Therefore, if you already use a particular citation style, especially the preferred style by scholars in a field related to the article you are editing, please use the citation style of your choice. However, if you can't decide on what style to use or if you don't know what information to include, an example style based on the APA style is given below. In APA style, a widely accepted format for writing research papers, the references are listed in alphabetical order by author, and by year for identical authors. Many other style guides, such as The Chicago Manual of Style's newer "Scientific format", use essentially the same style.

Books

• Lincoln, Abraham; Grant, U. S.; & Davis, Jefferson (1861). Resolving Family Differences Peacefully (3rd ed.). Gettysburg: Printing Press. ISBN 0-12-345678-9.

For an edited book, put "(Ed.)" or "(Eds.)" in parentheses after the last author, before the date. The ISBN (which is wikified automatically) is optional.

For a specific article or chapter in an edited book, use:

• Pooh, Winnie T. & Robin, Christopher (1926). Modern techniques in heffalump capture. In A. A. Milne (Ed.), The Karma of Kanga, pp. 23–47. Hundred Acre Wood: Wol Press.

A good guideline is to list author names as they are written in the original article/book, without using any abbreviations. The APA guidelines recommend abbreviating first names to initial letters instead, but since Wikipedia has no shortage of space, you need not abbreviate names. Indeed, there are good reasons to include the full names of authors; such information makes it much easier to find the cited work, and it also makes it possible to find other related information by the same author.

If Wikipedia has a page for the book, make the book title a link to it, but retain the full reference (e.g. for printing). If the authors are notable (as above) and have not already been linked to from the article, then make their names link to their pages. It is also occasionally relevant to link a publisher, place of publication, etc.

Journal articles

Journal articles are formatted much like a chapter in a book would be, e.g.:

• Brandybuck, Meriadoc. (1955). Herb-lore of the Shire. Journal of the Royal Institute of Chemistry 10 (2), 234–351.

Note that the numbers after the journal title indicate: volume (issue number, optional), page numbers. Do not capitalize every word of the article title, only the first word, proper names, and the first word after a colon/period/dash. For an article that is available online, make the article title a link to the online version.

It is questionable whether one should abbreviate journal titles. On the one hand, many abbreviations are standardized ("J." for "Journal of") and library catalogs are often designed to help one look up abbreviated titles. On the other hand, abbreviations can be obscure to a person unused to scientific citations.

Newspaper/magazine articles (or online periodicals)

• Blair, Eric Arthur (Aug. 29, 1949). Looking forward to a bright tomorrow. New English Weekly, p. 57.

Or, for articles without a named author, put the title first:

• On the importance of modesty (May 5, 1821). Pravda, pp. B1, C12.

Again, for online articles, make the article title a link to the URL; it may not be possible to supply a page number in this case, e.g.:

• Chalmers, Rachel (Sep. 1, 2000). Guru of the Unix gurus (http://dir.salon.com/tech/feature/2000/09/01/rich_stevens/index.html). Salon.

Web sites and articles (not from periodicals)

To cite an entire Web site, without specifying a specific document on the site, simply give the site's URL in the article text (this is an APA recommendation). In Wikipedia, a simple URL beginning with "http://" is automatically rendered clickable as well, which is what you want. Here's an example of such text: "Slashdot is a popular web site at http://slashdot.org/ ". Since you're referring to a general website, and not any particular content on it, you do not need to give a retrieval date.

Specific web pages (or sets of pages) are cited like books are (and you make the title a link), but with a retrieval date:

• Gates, Bill & Ballmer, Steve (1998). The Big Open-source Advocacy Homepage (http://www.opensource.org/halloween/halloween1.php). Retrieved Aug. 5, 2003.

The parenthesized date should be the date/year the document was created, or last edited; this should be omitted if it cannot be determined. The "Retrieved" information helps a reader retrieve the same version that the writer viewed, using tools such as the Internet Archive.

Note that it is a common alternative in Wikipedia to have a section labelled External links (after the References) and list various links to other sites and to pages within them.

Other-language wikipedias

When you use an article from a different-language Wikipedia as a reference, it belongs in the reference section. Use an external link rather than an interwiki link to avoid an unnecesary self-reference:

• Citau les fonts (http://ca.wikipedia.org/wiki/Viquipèdia:Citau_les_fonts) from the Catalan-language Wikipedia. Retrieved December 27, 2004.

If you are getting some or all of your references second-hand, because you translated all or part of an article from a different-language Wikipedia, you may want to start your reference section (or part of it) with something like this (from Paragraph 175):

• Much of the content of this article comes from the equivalent German-language wikipedia article (http://de.wikipedia.org/wiki/Paragraph_175). The following references are cited by that German-language article:

followed by a list of that different-language article's references.

Company press releases

This is how to reference a company publication:

• Siemens AG (July 13, 1999). Shell and Siemens to develop emission-free fuel cell power plant (http://www.siemens.com/page/1,3771,229910-1-11_0_0-0,00.html). Press Release.

If the press release is also available online, make the title a link to the URL.

Notes

Example APA styles for many other document types can be found at the "Citation Style Guides" page (http://library.concordia.ca/help/howto/citations.html). Ultimately, though, use your common sense — what information does the reader need in order to find the reference in question?

Page ranges should use an "en" dash (–, –), not a hyphen (_).

It is also useful to link author names to their Wikipedia page [if any], assuming that they haven't already been linked to in the article text, to give background information on sources and other works they may have written.

Citation templates

The following templates have been implemented towards making following the above citation styles easier. These are in the process of being expanded to cover all categories defined above. Whether they are preferable to "plain_text" citations, as above, however, is left to the writer's discretion.

These are examples of how to use templates to cite books, journals, and web sites (other citation types to come):

Numbered footnotes for external citations

Footnotes are sometimes useful for relevant text that would distract from the main point if embedded in the main text, yet are helpful in explaining a point in greater detail. This is how footnotes are used in legal writings; see any supreme court decision, for example, Texas vs. Johnson (http://wikisource.org/wiki/Texas-v.-Johnson). Some articles may call out for a two_level text involving both a main text and extensive commentary, such as those found in legal writing or annotated historical or literary texts. Such footnotes can be especially helpful for later fact_checkers, to ensure that the article text is well_supported. Thus, using footnotes to provide useful clarifying information outside the main point is fine where this is needed.

Footnotes can also be used to simply cite sources, and there are some styles which do so. However, citations using numbered footnotes are controversial in Wikipedia for several reasons:

1. The current MediaWiki software does not support footnotes well. In particular, the software does not support automatic renumbering of arbitrary footnotes other than bare URLs inside single square brackets, so modifying footnotes may involve hand renumbering of many footnotes. This is a laborious and error_prone process; errors are difficult to detect, and once an error is made it can be difficult (even using history information) to correct. Even bare URLs in single square brackets, which are at least automatically numbered, are not really handled correctly: if the same URL occurs more than once, each citation is still given a different number. In contrast, the software is currently quite sufficient to support the parenthetical author citation format suggested above.
2. Many of today's style guides forbid or deprecate footnotes and reference endnotes when used simply to cite sources (Concordia Libraries). The author_date reference system is, according to the Oxford Guide to Style, "the most commonly used reference method in physical and social sciences. It provides the author's name and year of publication within parentheses in the text, and the full details at the end of the work in a list of references. It is in contrast to the author_title (short_title) system, which provides this information with a combination of footnotes or endnotes and the full reference at the end of the work." The APA style, which is the basis of the current suggested Wikipedia source citation format, does not use footnotes to cite sources. The MLA style manual has deprecated reference footnotes and reference endnotes for decades in favor of in-line bibliographic references using author references.
3. Footnotes and endnotes are normally simply numbered numerically. Thus, determining who said what typically requires a reader to continually jump back and forth between the main body and the footnote/endnote to see if there is something of value. When footnotes are simply providing a much more detailed argument, this is often not a problem, but if the footnotes are the primary citation method, this can be critical (since it is sometimes important to keep track of who claims what).

Note, however, that it is far more important to have citations than to worry about whether a footnote or an author-year format is used. In certain fields, the normal style of citation is through footnotes. The Chicago Manual of Style, for example, has a newer "Scientific" format (using author-date) and a traditional "Humanities" format that uses footnotes. And in particular, it is better to have footnote citations than no citations.

More information on footnotes can be found in the Manual of Style - Footnotes. The article Wikipedia:Footnote2 describes a simple template for implementing footnotes, namely, entering {{fn|1}} at the footnote location, and {{fnb|1}} at the list of notes. Note that this still requires manual renumbering at this time when a footnote is changed.

Embedded HTML links for citations

The WikiMedia software supports embedding HTML links directly into an article. Simply using a bare URL (surrounded by whitespace) will cause the URL to be hyperlinked, but since some URLs are very long, this can make the result difficult to read. A more common alternative is to use a single square bracket, e.g., [http://www.google.com/ Google's web site]. If only the URL is provided, those URLs are automatically numbered (making it appear like a footnote); an example would be [http://www.google.com/].

An advantage of these embedded links is that it is easy for an online reader to click on the link and jump immediately to the cited article, if the article is still at the given URL and still contains the cited information. Another advantage of these embedded links is that they are very easy to create and maintain.

There are several disadvantages with such embedded links, however. Such links do not normally provide all the information that a traditional citation would have; thus, if the material moves or is dramatically changed, it can be very difficult to rediscover the cited material. If all that citation information is included in the embedded text, the result is unwieldy text.

Automatically-numbered links have some additional problems. Automatically-numbered links provide no information to the reader before moving the mouse to the link, so it can be difficult to determine if the same author is referenced in different citations or not. Also, there is a limitation of the WikiMedia software: if the same URL is referenced multiple times, each citation is given a different number; this means that a reader generally has no idea when the same article is referenced multiple times.

Again, it is far more important to cite sources than worry about formatting. If the choice is between using this format and not citing sources, please cite sources. There are a number of articles which do use the format of embedded hypertext links, e.g., Internet Explorer.

Amount of citation detail

A citation should include enough information to allow a reader to find your sources. In particular, be sure to give page numbers or section numbers of a lengthy work if only a small portion is referenced (and it's not immediately obvious where to look). Sometimes, you may want to give a more complete explanation of how you know something, or why your sources are credible. If the issue is important, please consider discussing that in the article itself. After all, other readers may need that information as well. Otherwise, you can leave a note on the article's talk page. This won't necessarily help readers, but it can help later Wikipedians trying to improve the article.

Citing Wikipedia

Inside a Wikipedia article, reference another Wikipedia article simply by surrounding its name with two square braces, e.g., [[Wikipedia]]. If this does not flow, use a renaming reference, e.g., [[Wikipedia|Wikipedia's contents]]. This is not considered an external reference, but it is very useful for readers. In general, only create a link to another Wikipedia article the first time a reference is made (though occasional exceptions for consistency or because it's a long article can be justified); otherwise, a page may be full of links and become difficult to read for some people.

Avoid duplicating references on a single topic unnecessarily — put the references in the most specific Wikipedia article on that topic, and not in other articles that link to that article. (Thus, for example, this article doesn't cite the APA, since there's a whole Wikipedia article on just that subject.)

For suggestions on how to cite Wikipedia in other works, see Wikipedia:Citing Wikipedia

See also

• Wikipedia:WikiProject Fact and Reference Check
• Weasel word

References

• Concordia Libraries (Concordia University). Citation and Style Guides (http://library.concordia.ca/help/howto/citations.html). Retrieved December 28, 2004. (This provides a list of common citation styles.)

See also Citation.