Wikimedia sister projects are all the publicly available wikis operated by the Wikimedia Foundation, including Wikipedia. This guideline covers Wikipedia's relations to the sister projects, including linking and copying content between a Wikipedia article and a sister project's article.

Wikipedia is written by volunteer editors and hosted by the Wikimedia Foundation, a non-profit organization that also hosts a range of other volunteer projects:

The above list of the current English language sister projects can be easily duplicated using the {{Wikipedia's sister projects}} template.

Wikipedia encourages links from Wikipedia articles to pages on sister projects when such links are likely to be useful to our readers, and interlingual crosslinking to articles on foreign-language editions of Wikipedia whenever such links are possible.

By far the most common use of links to the non-Wikipedia sister projects is the use of images that are stored on the Wikimedia Commons site (see Wikipedia:Wikimedia Commons).

For example:

Links to sister projects are made in several ways:

• by linking images and other files hosted by Commons. See Wikipedia:Picture tutorial for more;
• through inline links such as this link to The Wind in the Willows ([[Wikisource:The Wind in the Willows|''The Wind in the Willows'']]);
• through templates, which may produce either larger boxes or simpler one-line links. See the next section for how and where to place them; Templates are found in Wikipedia:Template messages/Sister projects and Category:Interwiki link templates;
• through standard links directly to the URL, exactly like any other website, such as The Wind in the Willows. However this form is deprecated in favour of links using [[sister-project:sister project name|display name]].

Sister project links should generally appear in the "External links" section, or where appropriate in citations. Two exceptions are links to Wiktionary and Wikisource that may be linked inline (e.g. to an unusual word or the text of a document being discussed).

Appropriate material from Wikimedia Commons may also be included within the main body of an article. See Embedding Commons' media in Wikipedia articles. Links to Wikinews should not be made within the main body of an article, being made only as per the external links guideline.

Most box-type templates such as {{Commons}} shown at right should be put at the beginning of the last section of the article (which is usually, but not necessarily, the "External links" section) so that boxes will appear next to, rather than below, the list items.^[a] Do not make a section whose sole content is box-type templates. Many box links can be unified to one by using {{Sister project links}} or {{Sister project}}.

Sometimes box-type templates are not aesthetically pleasing, either because there are no external links except sister project ones, or because they result in an odd layout, such as a long sequence of right-aligned boxes hanging off the bottom of the article or excessive white space when the section is laid out in columns. In such cases, consider using "inline" templates, such as {{Commons-inline}}, in the "External links" section, so that links to sister projects appear as list items, like this:

• Media related to Wikimedia Foundation at Wikimedia Commons

Sister project links are normally made only once within an article, as with standard links to other Wikipedia articles.

Sometimes an entry is more appropriate on some other sister project than on Wikipedia because they are of a non-encyclopedic scope (e.g. they can never be expanded beyond a simple dictionary definition, or call for a level of detail more appropriate to a textbook). Normally, such articles are copied to the more appropriate sister using the transwiki process, and deleted from Wikipedia afterwards.

However, if a word or phrase is commonly wikified, it is quite likely that the deleted entry will be quickly re-created again by well-meaning users. The re-created article is likely to again become non-encyclopedic.

To avoid this, do seek deletion of the page (or suppress after transwiki'ing). One solution, as suggested by Wikipedia deletion policy, is to instead normally redirect the word to a relevant article within Wikipedia. For instance, Organize could redirect to a well-developed Organization article via #REDIRECT [[Organization]].

If this is not possible, turn a Wikipedia page into a soft redirect to a sister project. The plain {{soft redirect}} template should not be used in the mainspace. Instead, use one of the specialized templates (see below). These templates inform readers of information on the sister project: in the case of this example, one link would be provided to the wikt:organize page. This has multiple benefits:

1. It brings the sister projects closer together
2. It prevents future clean-up issues

Please keep in mind that only topics with a less-than-encyclopedic scope that are commonly wikified words or that are repeatedly recreated should become soft redirects. We don't need a soft redirect for every possible word or phrase to be included in Wikipedia.

• {{Wikidata redirect}}; Category:Soft redirects connected to a Wikidata item – a special redirect category template

Mainspace exclusive

• {{Wiktionary redirect}}; Category:Redirects to Wiktionary
• {{Wikibooks redirect}}; Category:Redirects to Wikibooks
• {{Wikinews redirect}}: Category:Redirects to Wikinews
• {{Wikiquote redirect}}; Category:Redirects to Wikiquote
• {{Wikisource redirect}}; Category:Redirects to Wikisource
• {{Wikispecies redirect}}; Category:Redirects to Wikispecies
• {{Wikivoyage redirect}}; Category:Redirects to Wikivoyage
• {{Commons redirect}}; Category:Redirects to Wikimedia Commons

Unified login is a mechanism which allows users to use a single login across the majority of the Wikimedia Foundation's sister projects. This allows users to maintain a consistent identity throughout Wikimedia, following a single sign-up. Other advantages of this mechanism include the removal of the threat that impersonation poses and the ability to visit many projects without having to go through the labors of logging in everywhere. Users can create a unified login by visiting Special:MergeAccount on a project where they already have an account, and following the prompts.

• List of Wikipedias
• Category:Interwiki link templates
• Category:Transwiki templates
• Help:Interlanguage links
• Help:Interwiki linking
• m:Interwiki map
• Wikipedia:List of templates linking to other free content projects