A citation, or reference,[1] uniquely identifies a source of information:Wikipedia

A citation, or reference,[1] uniquely identifies a source of information:Wikipedia's Verifiability policy requires inline citations for any material challenged or likely to be challenged, and for all quotations, anywhere in article space.A citation or reference in an article usually has two parts. In the first part, each section of text that is either based on, or quoted from, an outside source is marked as such with an inline citation. The inline citation may be a superscript footnote number, or an abbreviated version of the citation called a short citation. The second necessary part of the citation or reference is the list of full references, which provides complete, formatted detail about the source, so that anyone reading the article can find it and verify it.This page explains how to place and format both parts of the citation. Each article should use one citation method or style throughout. If an article already has citations, preserve consistency by using that method or seek consensus on the talk page before changing it (the principle is reviewed at WP:CITEVAR). While you should try to write citations correctly, what matters most is that you provide enough information to identify the source. Others will improve the formatting if needed. Wikipedia:Referencing for beginners provides a brief introduction on how to reference Wikipedia articles.By citing sources for Wikipedia content, you enable users to verify that the information given is supported by reliable sources, thus improving the credibility of Wikipedia while showing that the content is not original research. You also help users find additional information on the subject; and you avoid plagiarising the source of your words or ideas by giving attribution.In particular, sources are required for material that is challenged or likely to be challenged – if reliable sources cannot be found for challenged material, it is likely to be removed from the article. Sources are also required when quoting someone, with or without quotation marks, or closely paraphrasing a source. However, the citing of sources is not limited to those situations – editors are always encouraged to add or improve citations for any information contained in an article.Citations are especially desirable for statements about living persons, particularly when the statements are contentious or potentially defamatory. In accordance with the biography of living persons policy, unsourced information of this type is likely to be removed on sight.For an image or other media file, details of its origin and copyright status should appear on its file page. Image captions should be referenced as appropriate just like any other part of the article. A citation is not needed for descriptions such as alt text that are verifiable directly from the image itself, or for text that merely identifies a source (e.g., the caption "Belshazzar's Feast (1635)" for File:Rembrandt-Belsazar.jpg).Citations are not used on disambiguation pages (sourcing for the information given there should be done in the target articles). Citations are often omitted from the lead section of an article, insofar as the lead summarizes information for which sources are given later in the article, although quotations and controversial statements, particularly if about living persons, should be supported by citations even in the lead. See WP:LEADCITE for more information.Inline citations allow the reader to associate a given bit of material in an article with the specific reliable source(s) that support the material. Inline citations are most commonly added using either footnotes (long or short) or parenthetical references (and the use of embedded links for inline citations is deprecated). This section describes how to add either type, and also describes how to create a list of full bibliography citations to support shortened footnotes or parenthetical references.If long or short inline citations placed in footnotes are used, the first editor to add footnotes to an article must create a section where the list of those citations is to appear. This is not necessary for inline parenthetical references, as these appear directly inline in the article prose.This section, if needed, is usually titled "Notes" or "References", and is placed at or near the bottom of the article. For more about the order and titles of sections at the end of an article (which may also include "Further reading" and "External links" sections), see Wikipedia:Footers.With some exceptions discussed below, citations appear in a single section containing only the <references /> tag or the {{reflist}} template. For example:The footnotes will then automatically be listed under that section heading. Each numbered footnote marker in the text is a clickable link to the corresponding footnote, and each footnote contains a caret which links back to the corresponding point in the text. Scrolling lists, or lists of citations appearing within a scroll box, should never be used. This is because of issues with readability, browser compatibility, accessibility, printing, and site mirroring.[2]If an article contains a list of general references, this is usually placed in a separate section, titled (for example) "References". This usually comes immediately after the section(s) listing footnotes, if any. (If the general references section is called "References", then the citations section is usually called "Notes".)To create a footnote, use the <ref>…</ref> syntax at the appropriate place in the article text, for example:which will be displayed as something like:It will also be necessary to generate the list of footnotes (where the citation text is actually displayed); for this, see the previous section.As in the above example, citation markers are normally placed after adjacent punctuation such as periods and commas. For exceptions, see the Punctuation and footnotes section of the Manual of Style. Note also that no space is added before the citation marker.The citation should be added close to the material it supports, offering text–source integrity. If a word or phrase is particularly contentious, an inline citation may be added next to that word or phrase within the sentence, but it is usually sufficient to add the citation to the end of the clause, sentence, or paragraph, so long as it's clear which source supports which part of the text.For multiple use of the same inline citation or footnote, you can use the named references feature, choosing a name to identify the inline citation, and typing <ref name="name">text of the citation</ref>. Thereafter, the same named reference may be reused any number of times by typing just <ref name="name" />.The text of the name can be almost anything‍—‌apart from being totally numeric. If spaces are used in the text of the name, the text must be placed within double quotes. Placing all named references within double quotes may be helpful to future editors who do not know that rule. To help with page maintenance it is recommended that the text of the name has a connection to the inline citation or footnote, for example "author year page": <ref name="Smith 2005 p94">text of the citation</ref>.If an article contains both footnoted citations and other (explanatory) footnotes, then it is possible (but not necessary) to divide them into two separate lists, using the grouping feature described in the Grouping footnotes section of the footnotes help page. The explanatory footnotes and the citations are then placed in separate sections, called (for example) "Notes" and "References" respectively.Inline references can significantly bloat the wikitext in the edit window and can become difficult and confusing. There are two main methods to avoid clutter in the edit window:As with other citation formats, articles should not undergo large-scale conversion between formats without consensus to do so.When an article cites many different pages from the same source, to avoid the redundancy of many big, nearly identical full citations, most Wikipedia editors use one of three options:The use of ibid., Id. (or similar abbreviations) is discouraged, as these may become broken as new references are added (op. cit. is less problematic in that it should refer explicitly to a citation contained in the article; however, not all readers are familiar with the meaning of the terms). If the use of ibid is extensive, use the {{ibid}} template.Some Wikipedia articles use short citations, giving summary information about the source together with a page number, as in <ref>Smith 2010, p. 1.</ref>. These are used together with full citations, which give full details of the sources, but without page numbers, and are listed in a separate "References" section. Short citations are used in articles which apply parenthetical referencing (see below), but they can also be used as footnote citations, as described here.Forms of short citations used include author-date referencing (APA style, Harvard style, or Chicago style), and author-title or author-page referencing (MLA style or Chicago style). As before, the list of footnotes is automatically generated in a "Notes" or "Footnotes" section, which immediately precedes the "References" section containing the full citations to the source. Short citations can be written manually, or by using the {{sfn}} or {{harvnb}} templates. (Note that templates should not be added without consensus to an article that already uses a consistent referencing style.) The short citations and full citations may be linked so that the reader can click on the short note to find full information about the source. See the template documentation for details and solutions to common problems. For variations with and without templates, see wikilinks to full references. For a set of realistic examples, see these.This is how short citations look in the edit box:This is how they look in the article:The Sun is pretty big,[1] but the Moon is not so big.[2] The Sun is also quite hot.[3]NotesReferencesShortened notes using titles rather than publication dates would look like this in the article:NotesWhen using manual links it is easy to introduce errors such as duplicate anchors and unused references. The script User:Ucucha/HarvErrors will show many related errors. Duplicate anchors may be found by using the W3C Markup Validation Service.While most articles use footnote citations as described in the above sections, some articles use a parenthetical referencing style. Here, short citations in parentheses, such as (Smith 2010, p. 1), are placed within the article text itself. Full details of each source used are given in a full citation, e.g., Smith, John. Name of Book. Cambridge University Press, 2010. The full citations are listed in alphabetical order, according to the authors' surnames, at the end of the article in a "References" section.Several forms of short citation are used in Wikipedia; see Short citations above. The inline citation and full citation may be linked using a template (see linking inline and full citations); as with other citation templates, these should not be added to articles without consensus.This is how it looks in the edit box:This is how it looks in the article:The Sun is pretty big (Miller 2005, p. 1), but the Moon is not so big (Brown 2006, p. 2). The Sun is also quite hot (Miller 2005, p. 3).ReferencesNotice that, unlike footnotes, parenthetical references are placed before adjacent punctuation such as commas and periods.A general reference is a citation to a reliable source that supports content, but is not linked to any particular piece of material in the article through an inline citation. General references are usually listed at the end of the article in a "References" section, and are usually sorted by the last name of the author or the editor.The appearance of a general references section is the same as those given above in the sections on short citations and parenthetical references. If both cited and uncited references exist, their distinction can be highlighted with separate section named, e.g., "References" and "General references".A general references section may also be included in an article that will eventually use inline citations throughout if such citations have not yet been given for all the information in the article. In underdeveloped articles, a general references section may exist even though no inline citations at all have yet been added, especially when all article content is supported by a single source. The disadvantage of using general references alone is that text–source integrity is lost, unless the article is very short.General references are frequently reworked by later editors into inline citations.Listed below is the information which a typical inline citation or general reference will provide, though other details may be added as necessary. This information is included in order to identify the source, assist readers in finding it, and (in the case of inline citations) indicate the place in the source where the information is to be found. (If an article uses parenthetical referencing or short citations, then the inline citations will refer to this information in abbreviated form, as described in the relevant sections above.)Since around 1970, a unique ISBN has been assigned to each English language edition and variation (except reprintings) of a book. It is acknowledged that there are (at least potentially) variations between editions as distinct from reprints that occur between editions. In effect, different editions of the same work can be considered different sources. A reprint in this context is distinctly different from a contemporary reprint of an historical publication (see Reprints of older publications). Reference details should include the edition (if not the first edition) and the date/year published reported is the year that the particular edition became available (see On the Origin of Species for an example that references multiple editions of the same work). Where publishers list multiple locations/offices on the title page, the location used is the first of these.Citations for books typically include:In some instances, the verso of a book may record, "Reprinted with corrections XXXX" or similar, where 'XXXX' is a year. This is a different version of a book in the same way that different editions are different versions. In such a case, record: the year of the particular reprint, the edition immediately prior to this particular reprint (if not the first edition) and an a note to say "Reprint with corrections". If {{cite}} (or similar) is being used, the notation, "Reprint with corrections", can be added immediately following the template. Reprints of older publications gives an example of appending a similar textural note.Citations for journal articles typically include:Citations for newspaper articles typically include:Citations for World Wide Web pages typically include:Citations for sound recordings typically include:Citations for films, TV episodes, or video recordings typically include:When citing lengthy sources, you should identify which part of a source is being cited.Specify the page number or range of page numbers. Page numbers are not required for a reference to the book or article as a whole. When you specify a page number, it is helpful to specify the version (date and edition for books) of the source because the layout, pagination, length, etc. can change between editions.If there are no page numbers, whether in ebooks or print materials, then you can use other means of identifying the relevant section of a lengthy work, such as the chapter number or the section title.In some works, such as plays and ancient works, there are standard methods of referring to sections, such as "Act 1, scene 2" for plays and Bekker numbers for Aristotle's works. Use these methods whenever appropriate.Specify the time at which the event or other point of interest occurs. Be as precise as possible about the version of the source that you are citing; for example, movies are often released in different editions or "cuts". Due to variations between formats and playback equipment, precision may not be accurate in some cases. However, many government agencies do not publish minutes and transcripts but do post video of official meetings online; generally the subcontractors who handle audio-visual are quite precise.A citation ideally includes a link or ID number to help editors locate the source. If you have a URL (webpage) link, you can add it to the title part of the citation, so that when you add the citation to Wikipedia the URL becomes hidden and the title becomes clickable. To do this, enclose the URL and the title in square brackets—the URL first, then a space, then the title. For example:For web-only sources with no publication date, the "Retrieved" date (or the date you accessed the webpage) should be included, in case the webpage changes in the future. For example: Retrieved 15 July 2011 or you can use the accessdate parameter in the automatic Wikipedia:refToolbar 2.0 editing window feature.You can also add an ID number to the end of a citation. The ID number might be an ISBN for a book, a DOI (Digital Object Identifier) for an article, or any of several ID numbers that are specific to particular article databases, such as a PMID number for articles on PubMed. It may be possible to format these so that they are automatically activated and become clickable when added to Wikipedia, for example by typing ISBN (or PMID) followed by a space and the ID number.If your source is not available online, it should be available in reputable libraries, archives, or collections. If a citation without an external link is challenged as unavailable, any of the following is sufficient to show the material to be reasonably available (though not necessarily reliable): providing an ISBN or OCLC number; linking to an established Wikipedia article about the source (the work, its author, or its publisher); or directly quoting the material on the talk page, briefly and in context.Google Books allows book pages to be linked to directly if both the book and the individual pages have been made available for preview. These can be written in a number of ways, with or without citation templates:In edit mode, the URL for p. 18 of A Theory of Justice looks like this:When the page number is a Roman numeral, commonly seen at the beginning of books, the URL looks like this for page xvii of the same book:You can also link to a tipped-in page, such as an unnumbered page of images between two regular pages. (If the page contains an image that is protected by copyright, it will be replaced by a tiny notice saying "copyrighted image.") The URL for eleventh tipped-in page inserted after page 304 of The Selected Papers of Elizabeth Cady Stanton and Susan B. Anthony, looks like this:Page links should only be added when the book is available for preview; they will not work with snippet view. Keep in mind that availability varies by location. No editor is required to add page links, but if another editor adds them, they should not be removed without cause; see the October 2010 RfC for further information.There is a tool available to help see: Wikipedia citation tool for Google Books.Links to long PDF documents can be made more convenient by taking readers to a specific page with the addition of #page=n to the document URL, where n is the page number. For example, using http://www.domain.com/document.pdf#page=5 as the citation URL displays page five of the document in any PDF viewer that supports this feature; otherwise, it goes to the first page.Note that this functionality depends on support from the web browser's PDF viewer. In some cases, the browser may ignore the PDF page specification and display the first page instead.A convenience link is a link to a copy of your source on a webpage provided by someone other than the original publisher or author. For example, a copy of a newspaper article no longer available on the newspaper's website may be hosted elsewhere. When offering convenience links, it is important to be reasonably certain that the convenience copy is a true copy of the original, without any changes or inappropriate commentary, and that it does not infringe the original publisher's copyright. Accuracy can be assumed when the hosting website appears reliable. Where several sites host a copy of the material, the site selected as the convenience link should be the one whose general content appears most in line with Wikipedia:Neutral point of view and Wikipedia:Verifiability.Don't cite a source unless you've seen it for yourself. If you want to cite John Smith, but you've only read Paul Jones who cites Smith, then write it like this (this formatting is just an example):John Smith, Name of Book I Haven't Seen, Cambridge University Press, 2009, p. 99, cited in Paul Jones, Name of Encyclopedia I Have Seen, Oxford University Press, 2010, p. 29.However, if you have read Smith's book yourself, you may cite it directly; there is no need to give credit to any sources, search engines, websites, library catalogs, etc., that led you to that book. You also do not need to specify how you obtained and read Smith's book; so long as you are confident that you read a true and accurate copy, it does not matter whether you read the book using an online service like Google Books, using preview options at a bookseller's website like Amazon, on an e-reader (except to the extent that this affects page numbering), through your library, with online paid databases of scanned publications, using reading machines, or any other method.Editors should be aware that older sources (especially those in the public domain) are sometimes reprinted with modern publication dates. When this occurs and the citation style being used requires it, cite both the original publication date, as well as the date of the re-publication. E.g.:This is done automatically in the {{citation}} and {{cite book}} templates when you use the |origyear= parameter.Alternately, information about the reprint can be appended as a textual note:In most cases it is sufficient for a citation footnote simply to identify the source (as described in the sections above); readers can then consult the source to see how it supports the information in the article. Sometimes, however, it is useful to include additional annotation in the footnote, for example to indicate precisely which information the source is supporting (particularly when a single footnote lists more than one source – see Bundling citations and Text–source integrity below).A footnote may also contain a relevant exact quotation from the source. This is especially helpful when the cited text is long or dense. A quotation allows readers to immediately identify the applicable portion of the reference. Quotes are also useful if the source is not easily accessible.In the case of non-English sources, it may be helpful to quote from the original text and then give an English translation. If the article itself contains a translation of a quote from such a source (without the original), then the original should be included in the footnote. See Non-English sources in the verifiability policy for more information.While citations should aim to provide the information listed above, Wikipedia does not have a single house style, though citations within any given article should follow a consistent style. A number of citation styles exist including those described in the Wikipedia articles for Citation, APA style, ASA style, MLA style, The Chicago Manual of Style, Author-date referencing, Vancouver system and Bluebook.Although nearly any consistent style may be used, avoid all-numeric date formats other than YYYY-MM-DD, because of the ambiguity concerning which number is the month and which the day. For example, 2002-06-11 may be used, but not 11/06/2002. The YYYY-MM-DD format should in any case be limited to Gregorian calendar dates where the year is after 1582.Editors should not attempt to change an article's established citation style merely on the grounds of personal preference, to make it match other articles, or without first seeking consensus for the change. As with spelling differences, it is normal practice to defer to the style used by the first major contributor or adopted by the consensus of editors already working on the page, unless a change in consensus has been achieved. If the article you are editing is already using a particular citation style, you should follow it; if you believe it is inappropriate for the needs of the article, seek consensus for a change on the talk page. If you are the first contributor to add citations to an article, you may choose whichever style you think best for the article.As noted above under What information to include, it is helpful to include hyperlinks to source material, when available. Here we note some issues concerning these links.Embedded links to external websites should not be used as a form of inline citation, because they are highly susceptible to linkrot. Wikipedia allowed this in its early years—for example by adding a link after a sentence, like this [http://media.guardian.co.uk/site/story/0,14173,1601858,00.html], which looks like this. [1] This is no longer recommended. Raw links are not recommended in lieu of properly written out citations, even if placed between ref tags, like this <ref>[http://media.guardian.co.uk/site/story/0,14173,1601858,00.html]</ref>. Since any citation that accurately identifies the source is better than none, do not revert the good-faith addition of partial citations. They should be considered temporary, and replaced with more complete, properly formatted citations as soon as possible.Embedded links should never be used to place external links in the content of an article, like this: "Apple, Inc. announced their latest product…".A convenience link is a link to a copy of your source on a webpage provided by someone other than the original publisher or author. For example, a copy of a newspaper article no longer available on the newspaper's website may be hosted elsewhere. When offering convenience links, it is important to be reasonably certain that the convenience copy is a true copy of the original, without any changes or inappropriate commentary, and that it does not infringe the original publisher's copyright. Accuracy can be assumed when the hosting website appears reliable. Where several sites host a copy of the material, the site selected as the convenience link should be the one whose general content appears most in line with Wikipedia:Neutral point of view and Wikipedia:Verifiability.If your source is not available online, it should be available in reputable libraries, archives, or collections. If a citation without an external link is challenged as unavailable, any of the following is sufficient to show the material to be reasonably available (though not necessarily reliable): providing an ISBN or OCLC number; linking to an established Wikipedia article about the source (the work, its author, or its publisher); or directly quoting the material on the talk page, briefly and in context.For a source available in hardcopy, microform, and/or online, omit, in most cases, which one you read. While it is useful to cite author, title, edition (1st, 2nd, etc.), and similar information, it generally is not important to cite a database such as ProQuest, EbscoHost, or JStor (see the list of academic databases and search engines) or to link to such a database requiring a subscription or a third party's login. The basic bibliographic information you provide should be enough to search for the source in any of these databases that have the source. Don't add a URL that has a part of a password embedded in the URL. However, you may provide the DOI, ISBN, or another uniform identifier, if available. If the publisher offers a link to the source or its abstract that does not require a payment or a third party's login for access, you may provide the URL for that link. If the source only exists online, give the link even if access is restricted (see WP:PAYWALL).To help prevent dead links, persistent identifiers are available for some sources. Some journal articles have a digital object identifier (DOI); some online newspapers and blogs, and also Wikipedia, have permalinks that are stable. When permanent links aren't available, consider archiving the referenced document when writing the article; on-demand web archiving services such as WebCite (http://www.webcitation.org) are fairly easy to use (see pre-emptive archiving).Dead links should be repaired or replaced if possible. Do not delete a citation merely because the URL is not working today. Follow these steps when you encounter a dead URL being used as a reliable source to support article content:When using inline citations, it is important to maintain text–source integrity. The point of an inline citation is to allow readers and other editors to check that the material is sourced; that point is lost if the citation is not clearly placed. The distance between material and its source is a matter of editorial judgment, but adding text without clearly placing its source may lead to allegations of original research, of violations of the sourcing policy, and even of plagiarism.Editors should exercise caution when rearranging or inserting material to ensure that text–source relationships are maintained. In particular, if a sentence or paragraph is footnoted with a source, adding material to that sentence which is not supported by the source is highly misleading. When new text is inserted into a paragraph, make sure it is supported. For example:The sun is pretty big.[1] The sun is also quite hot.[2]NotesDo not add other facts or assertions into a fully cited paragraph or sentence:NThe sun is pretty big, but the moon is not so big.[1] The sun is also quite hot.[2]NotesInclude a source to support the new information. There are several ways to write this, including:YThe sun is pretty big,[1] but the moon is not so big.[2] The sun is also quite hot.[3]NotesSometimes the article is more readable if multiple citations are bundled into a single footnote. For example, when there are multiple sources for a given sentence, and each source applies to the entire sentence, the sources can be placed at the end of the sentence, like this.[4][5][6][7] Or they can be bundled into one footnote at the end of the sentence or paragraph, like this.[4]Bundling is also useful if the sources each support a different portion of the preceding text, or if the sources all support the same text. Bundling has several advantages:When formatting multiple citations in a footnote, there are several layouts available, as illustrated below. Within a given article, only a single layout should be used.The sun is pretty big, but the moon is not so big. The sun is also quite hot.[1]NotesParagraphIn-text attribution is the attribution inside a sentence of material to its source, in addition to an inline citation after the sentence. In-text attribution should be used with direct speech (a source's words between quotation marks or as a block quotation); indirect speech (a source's words modified without quotation marks); and close paraphrasing. It can also be used when loosely summarizing a source's position in your own words. It avoids inadvertent plagiarism and helps the reader see where a position is coming from. An inline citation should follow the attribution, usually at the end of the sentence or paragraph in question.For example:When using in-text attribution, make sure it doesn't lead to an inadvertent neutrality violation. For example, the following implies parity between the sources, without making clear that the position of Darwin is the majority view:Neutrality issues apart, there are other ways in-text attribution can mislead. The sentence below suggests The New York Times has alone made this important discovery:It is best not to clutter articles with information best left to the references. Interested readers can click on the ref to find out the publishing journal:Simple facts such as this can have inline citations to reliable sources as an aid to the reader, but normally the text itself is best left as a plain statement without in-text attribution:If an article is unreferenced, you can tag it with the {{unreferenced}} template, so long as it is not nonsensical or a biography of a living person, in which case request admin assistance.Citation templates can be used to format citations in a consistent way. The use of citation templates is neither encouraged nor discouraged: an article should not be switched between templated and non-templated citations without good reason and consensus – see Variation in citation methods above.If citation templates are used in an article, the parameters should be accurate. It is inappropriate to set parameters to false values in order that the template will be rendered to the reader as if it were written in some style other than the style normally produced by the template (e.g., MLA style).Citations may be accompanied by metadata, though it is not mandatory. Most citation templates on Wikipedia use the COinS standard. Metadata such as this allow browser plugins and other automated software to make citation data accessible to the user, for instance by providing links to their library's online copies of the cited works. In articles that format citations manually, metadata may be added manually in a span, according to the COinS specification.You can insert a link beside each citation in Wikipedia, allowing you to export the citation to a reference manager such as EndNote. To install the script just add the following line to Special:MyPage/skin.js (applies to the currently selected skin) or Special:MyPage/common.js (applies to all skins)"Then save the page and follow the instructions at the top of that page to bypass your browser's cache.Reference management software can output formatted citations in several styles, including BibTeX, RIS, or Wikipedia citation template styles.How to citeCitation problemsChanging citation style formats