Cross-namespace redirects are redirects from one namespace to another. The term is most often applied to redirects from the main (article) namespace to the Wikipedia (project) namespace. There have been various debates over the use of cross-namespace redirects, and the issue remains moderately controversial.

Currently, the general consensus seems to be that most newly created cross-namespace redirects from the main (article) namespace to the Wikipedia (project) namespace should be deleted, that very old ones might retain their value for extra-Wikipedia links. Redirects from mainspace to Draftspace or Userspace are normally speedy deleted. Similarly redirects from Portal namespace to Draft caused by moves are deleted because we don't want to lead readers into areas where pages are under construction.

Latest relevant discussion: Wikipedia:Village pump (policy)/Archive 112#RFC: On the controversy of the pseudo-namespace shortcuts, December 2013 – February 2014

Cross-namespace redirects from mainspace to userspace and draftspace are rapidly deleted per WP:CSD#R2.

R2. Cross-namespace redirects
This applies to redirects (apart from shortcuts) from the main namespace to any other namespace except the Category:, Template:, Wikipedia:, Help: and Portal: namespaces.

Many of these arguments concern mainly redirects from the article namespace to organisational namespaces, like Wikipedia or Template; they may not be as applicable to redirects to other content namespaces, like Category. Also, while redirects from Wikipedia namespace to, say, Template are technically cross-namespace, they do not break the division between encyclopaedic content and organisational side of the project, and therefore their existence does not generally raise objections.

Related guidelines: Wikipedia:Avoid self-references, Wikipedia:Redirects#Reasons for deleting (reason #6), Wikipedia:Verbatim copying

1. CNRs are bad because they result in a person (reader) walking around a museum (encyclopedia) and falling through a trapdoor into a staff-only area (project space) because the curators (editors) thought secret doors and false floors would be useful for them to get around.
2. Namespaces were created for a reason, so that the encyclopedic content would be separate. CNRs work against this.
3. The filters in the Wikipedia search function exist for a reason, to fine-tune search results. Some encyclopedic searches results wind up featuring a large number of Wikipedia namespace pages due to cross-namespace redirects; making the reader user weed through them manually. Search filters should work, not return extraneous results. (For example, searching the encyclopedia for a term "page update" (which is hardly a Wikipedia specific term) will return CNRs as the first four results, and we should not be requiring readers to sift through non-encyclopedic background noise when they were explicitly searching the encyclopedia.) For the reader who has deliberately unselected the box because they don't want Wikipedia namespace results, it is unfair to return them anyway. With CNRs, a reader can choose to search Wikipedia by ticking the box, but they have no option not to do so. Without CNRs, readers wishing to search Wikipedia namespace can do so, and those who do not want to can also do so. Thus, the existence of CNRs removes choice.
4. Some mirrors duplicate the main article namespace but not the project namespace. Thus, cross-namespace redirects end up creating thousands of broken links on mirrors. Per Wikipedia:Self-references to avoid we should link to stuff outside of the article namespace with external links; see Wikipedia as an example.
5. Some CNRs result from moving fledgling articles to the Draft namespace for incubation. The resulting redirect then points readers to a draft article that is not ready for inclusion in the encyclopedia, which is not ideal. Once the draft is brought up to a standard for article status, an administrator must then delete the redirect in order to allow the draft to be moved back to the article namespace, requiring additional effort in listing the technical move request and waiting for intervention by busy administrators.

Related guideline: Wikipedia:Redirects#Reasons for not deleting reason #5

1. For redirects which have been extensively used on Talk and User pages, the cost of orphaning the redirect is high.
2. Useful to some people. One purpose of WP is to explain obscure references.
3. Many CNRs are very unlikely search terms when looking for articles anyway. If someone searches for "articles for deletion", it's only logical that they are looking for Wikipedia:Articles for deletion, and not for any encyclopedia article. This is essentially a counter-argument to the first argument for deleting CNRs.
4. Otherwise the newbie users for whom these redirects are useful would be left up the creek. In most cases, users who type such names in the search box expect to be taken to its other-namespace target. New users can't be expected to know to add "WP:" to their search.
5. CNRs aid in accidental linking.
6. They're easier to type.
7. If they're acceptable, then Wikipedia requires no policy on cross-namespace redirects. Simplifying policy improves odds that newbies and policy non-wonks understand/follow policy.
8. Often, the redirect is a holdover from before the creation of the alternate namespace version. The redirect may hold history of the page. (WP:R reason #1)
9. Redirects that are used exclusively on User, Talk, and other project pages do not create confusion. Readers of the article-space only (whether at Wikipedia or through a mirror that copies only our article-space) are unlikely to fall "backstage", because these "trapdoors" (or more accurately, "access ports") are only being left in the maintenance areas.

• Currently the default search filter is set to main namespace only.
• Wikipedia has many more readers than editors.
• Currently, many disambiguation links have entries that point to the Wikipedia namespace, serving the same function as cross-namespace redirects.
• In some cases an encyclopedic article may be written on the Wikipedia topic such as Deletion of articles on Wikipedia of which the likes of Articles for deletion redirects to, a hatnote may then direct to the project space.

• Category:Cross-namespace redirects