WP : CITE A citation is a line of text that uniquely identifies a . For example : When to cite sources : The policy on sourcing is , which requires for any material challenged or likely to be challenged , and for all quotations . The policy is strictly applied to all material in the mainspace — articles , lists , and sections of articles — without exception , and in particular to : unsourced contentious or negative material about living persons must be removed immediately . When an image is uploaded , the uploader must state where the image came from , and its copyright status . If the image comes from an online site , a link to the source page is normally provided . How to write citations : While you should try to write citations correctly , what matters is that you add your source — provide enough information to identify the source , and others will improve the formatting if needed . Each article should use the same citation method throughout . If an article already has citations , adopt the method in use or seek before changing it . In the event of a contradiction between this page and the sourcing policy , , the policy takes priority , and this page should be updated to reflect it . Use of terms . A " citation " is a line of text that identifies a source . The word " source " has three related meanings on Wikipedia : the piece of work itself , the creator of the work , and the publisher of the work ; see . The word " reference " may refer to the citation , the source , or both . A common system of citation on Wikipedia is a footnote system , where citations appear in footnotes . The terms " footnote " and " note " are used interchangeably . There is no separate usage of the term " endnote , " because each Wikipedia article , like other HTML documents , is considered to be only one page even if it is displayed across several screens . The terms " Further reading " and " External links " are used as section headings for lists of additional general texts on a topic for those interested . Summary . Footnote referencing is the most common method for citing sources in Wikipedia . The basic steps are : It is usually sufficient to add footnotes after the sentence or paragraph to which the citation applies . If the issue is very contentious , footnotes can be added immediately after the word or clause they support . , but normally the footnote is placed immediately " after " any punctuation marks that directly follow the word , clause , or sentence . Why and when to cite sources . Wikipedia is written by contributors with a wide range of knowledge and skills . Readers need to be able to check the contributors ' sources . Adding citations ( references ) : When adding material that is challenged or likely to be challenged . says : " All quotations and any material challenged or likely to be challenged should be attributed to a reliable , published source using an inline citation . " The need for citations is especially important when writing about opinions held on a particular issue . where possible , such as , " Some people say . . . " Instead , make your writing : find a specific person or group who holds that opinion and give a citation to a reputable publication in which they express that opinion . Remember that Wikipedia is not a place for expressing your own opinions or for . Opinions , data and statistics , and statements based on someone ' s scientific work should be cited and attributed to their authors in the text . When quoting someone . You should always add a citation when quoting published material , including the page number if there is one . The citation should be placed either directly after the quotation or after a sentence or phrase that introduces the quotation . For statements about which reliable sources are in conflict , the text should clearly attribute the opinions . When writing about living persons . Statements about living persons should be sourced with particular care , for legal and ethical reasons . All contentious material about living persons must cite a . If you find unsourced or poorly sourced contentious material about a living person , whether in an article or on a talk page , remove it immediately ! Do not leave it in the article while you request a source . Do not move it to the talk page . This applies whether the material is in a biography or any other article . When checking content added by others . You can also add sources for material you did not write . Adding citations is an excellent way to contribute to Wikipedia . See for organized efforts to add citations . Dealing with unsourced material . If an article has no references , and you are unable to find any yourself , you can tag the article with the template , so long as it is not nonsensical or a , in which case request admin assistance . When writing an image caption . Image within articles , also known as cutlines , should be referenced , if needed , just like any other part of the text . When uploading an image . Images must include source details and a on the image description page . It is important that you list the author of the image if known ( especially if different from the source ) , which is important both for copyright and for informational purposes . Some copyright licenses require that the original author receive credit for their work . Any image with a non - free copyright license must be accompanied by a " " ( also called a " fair use rationale " ) for each article in which the image is used . How to present citations . Citations are usually presented within articles in one of five ways : The full citation will appear in an appendix to the article . If this appendix does not already exist , create the appendix and place either < nowiki > < / nowiki > or in it . This will automatically generate the list of footnotes . The example below shows what this would look like in the edit box : The Sun is pretty big , < ref > Miller , E : < nowiki > " The Sun " < / nowiki > , page 23 . Academic Press , 2005 . < / ref > but the Moon is not so big . < ref > Brown , R : " Size of the Moon " , < nowiki > " Scientific American " < / nowiki > , 51 ( 78 ) : 46 < / ref > The Sun is also quite hot . < ref > Miller , E : < nowiki > " The Sun " < / nowiki > , page 34 . Academic Press , 2005 . < / ref > Notes . < nowiki > < / nowiki > Below is how this would look in the article , once you had previewed or saved your edited section : The Sun is pretty big , but the Moon is not so big . The Sun is also quite hot . Notes Where the issues are not contentious , you can combine references to avoid clutter : The Sun is pretty big , but the Moon is not so big . The Sun is also quite hot . Notes Shortened footnotes . Many articles use shortened citations in footnotes , giving just the author , year ( or title ) and the page numbers . As before , the list of footnotes is automatically generated in a " Notes " or " Footnotes " section . A full citation is then added in a " References " section . The short citation and the full citation may be linked so that the reader may click on the short note to highlight the full citation ( see wikilinks to full references ) . Short citations can be written manually , or by using the or templates , though note that templates should not be added without consensus to an article that already uses a consistent referencing style . Shortened footnotes are used for several reasons : they allow the editor to cite many different pages of the same source without having to copy the entire citation ; they avoid the inevitable clutter when long citations are inserted into the source text ; they bring together all the full citations into a coherent block of code ( rather than being strewn throughout the text ) which allows the list to be alphabetized and makes it easier to edit all the full citations at once ( e . g . , adding ISBN , DOI or other detail ) ; and a single footnote can contain multiple citations , thus avoiding long rows of footnote markers . Below is an edit - mode view of short footnotes : The Sun is pretty big , < ref > < nowiki > Miller 2005 < / nowiki > , p . 23 . < / ref > but the Moon is not so big . < ref > < nowiki > Brown 2006 < / nowiki > , p . 46 . < / ref > The Sun is also quite hot . < ref > < nowiki > Miller 2005 < / nowiki > , p . 34 . < / ref > Notes . < nowiki > < / nowiki > References . < nowiki > * < / nowiki > Brown , R ( 2006 ) . " Size of the Moon " , < nowiki > " Scientific American " < / nowiki > , 51 ( 78 ) . < nowiki > * < / nowiki > Miller , E ( 2005 ) . < nowiki > " The Sun " < / nowiki > , Academic Press . Below is how this would look once the edit has been saved : The Sun is pretty big , but the Moon is not so big . The Sun is also quite hot . Notes References Shortened notes using titles rather than publication dates could look like this in the article : Notes For more detailed examples using shortened notes , including the use of links from the short notes to the full references , see . List - defined references . As of September 2009 , the Cite . php extension was modified to suport list - defined references . These can be implemented with the parameter to the template , or by using a pair of HTML tags ( codice _ 1 ) in place of the codice _ 1 tag . These reduce clutter within articles , by putting all the citation details in the section at the end where the footnotes are displayed . As with other citation formats , these should not be added to articles that already have a stable referencing system , unless there is consensus to do so . When in doubt , use the referencing system added by the first major contributor to use a consistent style . The example below shows what list - defined references look like in the edit box : The Sun is pretty big , < ref name = Miller2005p23 / > but the Moon is not so big . < ref name = Brown2006 / > The Sun is also quite hot . < ref name = Miller2005p34 / > Notes . < nowiki > < / nowiki > Below is how this would look in the article , once you had previewed or saved your edited section : The Sun is pretty big , but the Moon is not so big . The Sun is also quite hot . Notes Defined references must be used within the body ; unused references will show an error message . However , non - list - defined references ( i . e . ordinary footnote references fully enclosed with < nowiki > < / nowiki > tags ) will display as normal along with any list - defined ones . Parenthetical referencing . Two forms of parenthetical referencing may also be used in Wikipedia : author - date referencing ( APA style , Harvard style , or Chicago style ) ; and author - title or author - page referencing ( MLA style or Chicago style ) . For a discussion of the advantages and disadvantages , see Pros & Cons . In parenthetical citations , a short version of the citation is added in parentheses just after the point it is supporting , comprising only the surname of the author ( s ) and the year of publication , and possibly page numbers ( APA style ) ; or the surname of the author ( s ) and possibly short titles and / or page numbers ( MLA style ) . Using author - date parenthetical references , the inline citation usually looks like : ( Author 2006 : 28 ) or ( Author 2006 , p . 28 ) . The full citation is then added at the end of the article to a " References " or " Works cited " section . This list of full citations is usually ordered alphabetically by author name . As with shortened notes , the inline citation and the full citation may be linked so that the reader may click on the inline citation to highlight the full citation ( see ) . Below is an edit - mode view of adding author - date citations to an article : The Sun is pretty big ( Miller 2005 ) , but the Moon is not so big ( Brown 2006 , p . 46 ) . The Sun is also quite hot ( Miller 2005 , p . 34 ) . References . < nowiki > * < / nowiki > Brown , R ( 2006 ) . " Size of the Moon " , < nowiki > " Scientific American " < / nowiki > , 51 ( 78 ) . < nowiki > * < / nowiki > Miller , E ( 2005 ) . < nowiki > " The Sun " < / nowiki > , Academic Press . Below is how this would look once the edit has been saved : The Sun is pretty big ( Miller 2005 ) , but the Moon is not so big ( Brown 2006 , p . 46 ) . The Sun is also quite hot ( Miller 2005 , p . 34 ) . References Embedded links . If a webpage is used as a source , it can be linked to directly within the article by enclosing the URL in square brackets just after the point it is supporting . When the edit is saved , only a number is visible within the text . For example , a citation of a newspaper article can be embedded by adding < nowiki > < / nowiki > , which looks like Embedded links should not be used to place to websites in the body of an article where they are " not " used to article content , but instead to direct readers to other websites . For example , do not spam links to companies ' or organizations ' websites in article text , like this : " Apple , Inc . announced their latest product . . . " Only links to pages that directly support claims made in the article should be embedded as links , and those embedded links should follow the formatting shown in the previous paragraph . to Wiktionary and Wikisource are sometimes appropriate in the body of an article ; for details , see . A full citation is also required in a References section at the end of the article . For example : codice _ 3 which appears as : Because of the difficulties in associating them with their appropriate full citations , the use of embedded links for inline citations is not recommended as a method of best practice and is not found in featured articles . It is easily converted to a shortened footnote or parenthetical reference . Say where " you " found it . It is improper to take material from one source and attribute it to a different one . For example , a webpage may provide information that the page ' s author attributes to a book . Unless you examine the book yourself , your source is the webpage , not the book . You should also make clear , where appropriate , that the webpage cited the book . It can be important to be clear about this for two reasons : ( a ) because the credibility of your edit rests on the webpage , which may have misinterpreted the book , and ( b ) because it is sometimes preferable to cite the original source , especially where the issue is a contentious one . For example , where Smith is the author of the book , and Jones the author of the webpage you have read , you could write : " Smith 2005 , p . 100 , cited in Jones 2010 , " between ref tags , with full citations in the References section . Or if you ' re using long citations in the text , you could write , again between ref tags : " Smith , John ( 2005 ) . " Name of Book " . Cambridge University Press , p . 100 , cited in Jones , Paul ( 2010 ) . " About Me , " " Pauljones . com " , accessed January 15 , 2010 . Note that it is always better to read the original source material yourself . Non - English sources . Because this is the English Wikipedia , English - language sources should be used in preference to non - English language sources of equal caliber and content , though the latter are allowed where appropriate . When quoting a source in a different language , please provide both the original - language quotation and an English translation , in the text , in a footnote , or on the talk page as appropriate . Convenience links . 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 and . Multimedia . Multimedia material should be referenced just like article text . Citations for a media file should appear on its . Image s should be referenced as appropriate just like any other part of the article . If an or contains text that needs citing , but the box or table cannot incorporate an inline citation , the citation should appear in a caption or other text that discusses the material . A citation is not needed for descriptions such as that are verifiable directly from the image itself . Material that identifies a source ( e . g . , the caption " " Belshazzar ' s Feast " ( 1635 ) " for " " ) is considered attribution and normally does not need further citation . Avoid scrolling lists . Scrolling lists , for example lists of citations appearing within a scroll box , should never be used because of issues with readability , , printing , and . Additionally , it cannot be guaranteed that such lists will display properly in all web browsers . See for more detail . How to format citations . Consistent style . Citations in Wikipedia articles should use a consistent style . Any of the following styles are acceptable so long as each article is internally consistent . You should follow the style already established in an article , if it has one ; where there is disagreement , the style used by the first editor to use one should be respected . Similarly , there are several methods of internal formatting or markup that can used to create a given displayed citation . The best practice is for a given article to be consistent in internal markup or formatting . It is better to follow the patterns in place if an article has a stable citation structure . Changing existing citations from one format to another should generally be done only with local consensus , and should never be the subject of an edit war . However , if an editor can provide a new relevant reference , either to new content or to existing unsourced content , it is more important for the citation to the reference to be recorded in some format . Another editor can always edit the reference to bring it into consistency with the style and formatting of the existing citations in the article . Citation styles . There are a number of citation styles . See for some examples . They all include the same information but vary in punctuation and the order of the author ' s name , publication date , title , and page numbers . Full citations for books typically include : Full citations for journal articles typically include : Citations for newspaper articles typically include : Citations for World Wide Web articles typically include : Identifying parts of a source . You should identify any part of a source that you quote , paraphrase or cite ; in the case of a book , specify the page number ( s ) . It is also important to specify the version ( date and edition for books ) of the source because the layout , pagination , length , etc can change . Page numbers are especially important for lengthy non - indexed books , but they are not required for a reference to the source as a whole ; for example when describing a complete book or article or when the source is used to illustrate a particular point of view . Links and ID numbers . 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 : codice _ 4 For web - only sources with no publication date you should include a " Retrieved " date instead , in case the webpage changes in the future . For example : 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 ) following by a space followed by 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 ) : 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 , and in context . Citation templates and tools . are used to format citations in a consistent way . The use of citation templates is neither encouraged nor discouraged . Templates may be used or removed at the discretion of individual editors , subject to agreement with other editors on the article . Because templates can be contentious , editors should not change an article with a distinctive citation format to another without gaining consensus . Where no agreement can be reached , defer to the style used by the first major contributor . There are several webpages / tools that can help quickly produce a citation in a standard template format . You may only need one piece of information and they can fill in the rest of the details . The resulting citation will be enclosed in " cite " tags , and it will be formatted in a particular way depending on which kind of template is being used . You can then copy all the text from there . It may still require additional tags before you can add it to a Wikipedia article . Metadata . Citations may be accompanied by metadata , though it is not mandatory . Most citation templates on Wikipedia use the COinS microformat . 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 ; or the templates or can be used . Citation export tools . You can insert a link beside each citation in Wikipedia , allowing you to export the citation to a reference manager such as EndNote . Just copy this code : to the end of . Then , save the page and . Preventing and repairing dead links . To help prevent , 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 permalink s 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 ) . If a dead link cannot be repaired or replaced , one option to consider is reworking the article section so that it no longer relies on the dead link , though this is not required . Regardless of whether a dead link can or cannot be repaired or replaced , remember that Wikipedia policy ( including policy on and ) still applies .