Interwiki linking can be a link to another project, to another language and both, to another project in another language.

• Interproject links: By adding a prefix to another Wikimedia project, internal link style ("prefixed internal link style") can be used to link to a page of another project. A system of short-handed link labels is used to refer to different projects, in the context of interproject linking, as seen within the actual source text.

For example, to link from here to the "surfeit" article on Wiktionary, you have to include the interwiki link [[wikt:surfeit]] which would appear as wikt:surfeit or the interwiki link [[wikt:surfeit|surfeit]] which would appear as surfeit.

• Interlanguage links: These are interwiki links linking different language editions of the same project. Wikimedia Projects with different language editions are:
  • Wikipedia
  • Wiktionary
  • Wikisource
  • Wikiquote
  • Wikibooks
  • Wikiversity
  • Wikivoyage
  • Wikinews
  There are two types of interlanguage links: those displayed in the page's languages dropdown menu and those displayed inline. Here an example for both types if placed in the English Wikipedia article Apple:
  1. [[fr:Pomme]]: This produces a link to the French Wikipedia article Pomme in the "Languages" menu of the page.  Note: Since 2013 this type of interlanguage link is usually centralized through Wikidata, which you can edit either by opening the Wikidata item, or selecting "Add language".
  2. [[:fr:Pomme]]: This produces an inline interlanguage link fr:Pomme in the English Wikipedia article.

This is called interwiki. For each project, an interwiki map (a list of target projects with their prefixes) is specified (Special:Interwiki). These target projects do not require MediaWiki and do not even have to be a wiki.

See also Wikipedia:Wikimedia sister projects #Linking between projects for a compact overview

Unless a language code is added, the following interwiki prefix codes link to the Wikiprojects in English.

Note that some links don't work as expected within the same project, e.g., meta:Test on Meta itself would mean m:Meta:Test, a different page. Outside of Wikimedia sister projects, only metawikipedia:Test might work for m:Test.

Wikimedia projects with different language editions are bold.

Other current Wikimedia prefixes: betawikiversity:, dbdump:, download:, gerrit:, mail:, mailarchive:, otrs:, OTRSwiki:, outreach:, quality:, rev:, spcom:, sulutil:, svn:, ticket:, tools:, tswiki:, wm2016:, wm2017:, wmania:, wikiconference:. See a complete list of current and old but still working prefixes for all Wikimedia wikis at the Special:SiteMatrix. See a complete list of all possible interwiki prefixes at Special:Interwiki.

Some of the long forms do not work as expected within the same project; for example [[meta:]] does not work on Meta, while [[metawikipedia:]] does. This depends on the configuration of the wiki and where the names are stored (see also next paragraph). The shortcuts work everywhere. The interwiki map on Meta lists many prefixes, among others, [[wikipedia:]] for the English Wikipedia, working from any Wiki supporting the Meta interwiki map, not only from MediaWiki wikis. Some prefixes work only with a page, for example: wikipediawikipedia: (fails) vs. wikipediawikipedia:Interwiki link (works). These prefixes are case insensitive.

The shortcuts are just interwikis with different histories. Wikipedia, Wikiquote etc. point to the English versions and are also included in the standard MediaWiki interwiki table (IIRC); w, q, b, wikt etc. are used like interlanguage wikilinks to link to the sisterproject in the same language (so w:it:b: is equivalent to Wikibooks:it:).

Non-Wikimedia interwiki codes have a limitation, that they can only be used through a link. For example, the entry for "John" on Wiktionary, a Wikimedia project, can be accessed by [[wikt:John]] or http://meta.wikimedia.org/wiki/wikt:John. However, the latter method does not work for non-Wikimedia wikis. For example, the main page on the Mozilla Wiki can be accessed via [[MozillaWiki:Main Page]], but http://meta.wikimedia.org/wiki/MozillaWiki:Main_Page results in an error. In these cases, Special:Search can be used (http://meta.wikimedia.org/wiki/Special:Search/MozillaWiki:Main_Page). You can see the Interwiki special page for a list of "forward" and "non-forward" prefixes.

Note that the section above includes two special versions of Wikipedia, nostalgia and test. Nostalgia is a static copy of Wikipedia, as it was in December 20, 2001 and can be linked to by using [[nost:]]. Test is a version of Wikipedia for edit and software testing and can be linked to by using [[testWiki:]].

Note that these shortcuts do not link to the versions of Wikipedia (or to other reader-focused, information-delivering projects such as Wiktionary) in languages other than English, but instead link to the localized equivalent of http://www.wikimedia.com (that is, modified for the local language, country or culture).

To suppress the first, visible prefix in the saved page, use the pipe trick: Add | at the end of the link, like this: [[s:test|]]. Upon saving your edits, it will be expanded to [[s:test|test]]. Note that this only works for the first prefix, so saving en:test, will automatically expand to [[s:en:test|en:test]], not to [[s:en:test|test]].

As demonstrated in the examples below, combinations of certain prefixes are allowed, thus enabling direct page links that are not possible with a single prefix. For example, by combining two prefixes, one can link a word in the English Wikipedia to a term in the German Wiktionary, or link to a category in the Commons.

When using language codes, the order of the prefixes does not matter. Remember to put a colon in front of a link starting with a language prefix; however, the colon is optional if the link starts with the project code prefix and then has the language prefix. See the last two examples in the table below.

When using the category prefix, the order of the prefixes does matter. The order must be [[project:category:category-name]]. Starting with a colon and the prefix category links to categories on this Wikipedia, creating a red link if the category doesn't exist. Without the colon but starting with the prefix category, nothing appears in the saved page.

A project's own namespace prefix cannot be reused as code for an external project. However, the prefix used for a target project may coincide with the prefix for a project namespace, within that project. As a result, to link to a page in that namespace, use the same prefix twice.

For portability across projects, one may want to select a link code that leads to the same target from all projects, for example: MetaWikipedia:wikibooks:Main Page. The "superfluous" "MetaWikipedia:" prevents "wikibooks:" being interpreted as namespace prefix, when the code is used at wikibooks itself, while at Meta the "MetaWikipedia:" is ignored (it is not a namespace prefix and even at Meta itself, it is recognized as code for Meta). The codes above work from all projects; however, the existence detection and the self-link feature do not work on interwiki links.

Interwiki links can use prefixes for the project and/or for the language. Without the prefix, links are local, for pages in the same project and the same language. If only a language is given, they go to a page in the same (or similar) project for the specified language:

[[:fr:]] fr:
[[:os:]] os:

If only the project is specified, they typically go to the language of the source, see above. At most, two prefixes are needed for pages in any existing project and any supported language:

[[s:de:Hauptseite]] s:de:Hauptseite
[[b:en:Main page]]  b:en:Main page

In the case of more than one prefix, a page name has to be specified. For example, while w: and en: from Meta lead to the English Wikipedia's main page, a bare [[w:en:]] does not work: w:en:.

If the language is different, specifying it before the project can also work:

[[:de:q:Hauptseite]] de:q:Hauptseite
[[:en:n:Main page]]  en:n:Main page
[[n:en:Main page]]   n:en:Main page

The second example doesn't work from English Wikipedia w:en: pages; a project prefix before the language is better.

More than two prefixes are generally unnecessary; the following examples should work everywhere:

[[m:Help:Help]] m:Help:Help
[[w:Interwiki]] w:Interwiki

Two prefixes can have unexpected effects; for example, from Meta, the following links end up on different pages:

[[m:en:About]]  m:en:About
[[:en:m:About]] en:m:About
[[m:About]]     m:About

In the first case Meta ignores the m:, because it is local and then, interprets en: as w:en:, the prefix for the English Wikipedia. In the second case, the leading en: goes to the English Wikipedia, where the following m: goes straight back to Meta. The second example doesn't work at all, from English Wikipedia w:en: pages, only the third example works everywhere.

In other words, multiple prefixes are evaluated left to right by the relevant Wikimedia servers (project and language). For projects without different languages, like Meta (because Meta is multilingual by itself), language prefixes can be handled as shorthands for w: plus the specified language:

[[:pl:2006]]   pl:2006
[[w:pl:2006]]  w:pl:2006
[[:pl:w:2006]] pl:w:2006

From Meta, the first two links both arrive at the Polish 2006 page. The third arrives at the English Wikipedia, because that's how the server selected by :pl: interprets the second prefix w:.

For a portable link on that server, it would be a bad idea to use w:, but :pl: does the trick. To test that effect from Meta, the following links should go to the same page:

[[:ja:2006]]    ja:2006
[[:ja:ja:2006]] ja:ja:2006

A universal interwiki link, that is, one that works no matter from which Wikimedia wiki, can be written [[m:project:language:page name]] (e.g. m:b:nl:Wiskunde); this routes the parsing of the links via Meta (bug 4285). m:mos:Soraogo links the mos Wikipedia. MOS is a namespace at the English Wikipedia so [[mos:Soraogo]] would be a local link.

Interlanguage links are links from any page (most notably articles) in one language edition of Wikipedia (or another Wikimedia project with different language editions) to one or more nearly equivalent or exactly equivalent pages in another language edition of the same Wikimedia project. As of February 2013, the use of "local" links for interlanguage linking has been deprecated, with interlanguage link data being centralized on Wikidata, a structured knowledge base project. Pages with their interlanguage links on Wikidata display an "Edit links" button under the language list.

 Note: The information below is deprecated, and kept for historical purposes.

Prior to February 2013, interwiki links were generated using "local" links within articles, taking the form [[language code:Title]], where the language code is the two-letter code as per ISO 639-1. (See Complete list of language Wikipedias available: English language is "en", German is "de", etc.) So, for example, in the English language article on plankton, which is available on many other wikis, the interlanguage links might look like this:

[[ar:عوالق]]
[[de:Plankton]]
[[eo:Planktono]]
[[es:Plancton]]
[[fr:Plancton]]
[[nl:Plankton]]
[[ja:プランクトン]]
[[ko:플랑크톤]]
[[pl:Plankton]]
[[pt:Plâncton]]
[[ru:Планктон]]
[[simple:Plankton]]
[[zh:浮游生物界]]

These links do not show up in the article, but instead populate the "Languages" list on the sidebar. While they can be theoretically located anywhere in the article, they were typically placed at the bottom.

Inline links to foreign-language Wikiprojects can be made by adding the language code as a prefix:

• To link to a Wikipedia article in a particular language inline (as opposed to the links in the sidebar), use [[:language code:Title]].
• To link to a page on a different project in a particular language, expand the above syntax with a code for the project from the table below in § Prefix codes for linking to projects, as in [[:project:language code:Title]] or [[:language code:project:Title]].

For example, [[:s:de:Salz]] or [[:de:s:Salz]] will link to the Salz page on the German-language Wikisource as de.wikipedia.org/wiki/s:Salz, [[:wikt:fr:sel]] or [[:fr:wikt:sel]] to the sel page on the French-language Wiktionary as en.wiktionary.org/wiki/fr:sel, etc. See § Doubling prefixes for more tips and examples, plus information on doubling with the category prefix.

For language codes, see list of Wikipedias. Remember to put a colon in front of a link starting with a language code prefix, or the saved edit will not show it at all; however, the colon is optional if the link starts with the project code prefix and then has the language code prefix.

The interlanguage link feature works on Wikimedia Commons and Wikispecies, producing links to the Wikipedias. This is not reciprocal, a link from a Wikipedia to Commons or Wikispecies is an in-page link.

To link from en.Wikipedia to the Chinese language Wikisource page 天問, but without the misleading and distracting appearance of an external link:

Type: [[s:zh:天問]] to get: s:zh:天問

Or, using piping, type: [[s:zh:天問|天問]] or [[s:zh:天問|Heavenly Questions]] to get: 天問 or Heavenly Questions

For an article that exists in German but not yet in English, use: {{interlanguage link|Gesellschaft Deutscher Naturforscher und Ärzte|de}} or {{ill|Gesellschaft Deutscher Naturforscher und Ärzte|de}} to get: Gesellschaft Deutscher Naturforscher und Ärzte [de]. Once the English article is written, the blue de link will disappear.

Disadvantages of interwiki links:

• The wikitext is less portable across wikis, because wikis do not always have an interwiki prefix for the same sites and even if they do, the prefixes may differ.
• There is no feature to find interwiki links, while searching for an external link can be done with Special:Linksearch. This is because, while there is an external links table, there is no such thing for interwiki links. The interwiki table only stores the interwiki prefixes with their targets as function of the parameter, not the instances of the links. Using the general text search, to search for interwiki links, is more work for the server and therefore, it may be slow, not up-to-date or in busy hours, disabled. See also: Finding external links to a page.

Comparison:

• [[imdbtitle:0389790|Bee Movie]] gives Bee Movie
• [https://www.imdb.com/title/tt0389790 Bee Movie] gives Bee Movie
  • Linksearch works for the latter only

The applicable CSS classes are "extiw" and "external text". The choice may be governed by this, either way, for uniformity or distinction. An interwiki link is easier to type by itself, but if one goes to the webpage anyways, before putting the link, copying the URL is very convenient. When a template is created, e.g. Template:IMDb title (backlinks ), the template can be made, such that it uses an interwiki link and a parameter, like "tt0389790" or "0389790", or that it uses an external link and a parameter like one of those or the full url, if that is more convenient.

Disadvantages of interwiki links to the same wiki, compared to internal links:

• no existence detection
• "What links here" works for internal links only

Advantages of interwiki links to the same wiki, compared to internal links:

• better portability across wikis, provided that the same prefix applies and is not equal to a namespace name

• Wikipedia:Wikimedia sister projects, a guideline for using Wikipedia's sister projects
• m:Templates for linking to sister projects
• Templates for linking between the various Wikimedia sister projects
  • {{Sister project links}}
  • Wikipedia:Template index/Sister projects
  • Category:Interwiki link templates
• Help:Interlanguage links, describes how to link between differing foreign language Wikipedias
• Help:Menu/Links, table of contents for help pages about links and references
• mw:Help:Interwiki linking, help page from MediaWiki
• Meta-Wiki content:
  • m:Help:Interwiki linking
  • m:Interwiki map, list of WMF and non-WMF mappings
• commons:Commons:First steps/Reuse, instructions on linking a file from Commons to Wikipedia
• Wikipedia:Help desk—To ask questions about using interwiki links in articles if you weren't able to find the information you need on this help page.