Wikipedia:Verifiability

The burden to demonstrate verifiability lies with the editor who adds or restores material

The cited source must clearly support the material as presented in the article. Cite the source clearly, ideally giving page number(s) – though sometimes a section, chapter, or other division may be appropriate instead; see Wikipedia:Citing sources for details of how to do this.

The word "source" when citing sources on Wikipedia has three related meanings:

If available, academic and peer-reviewed publications are usually the most reliable sources in topics such as history, medicine, and science.

Editors may also use material from reliable non-academic sources, particularly if it appears in respected mainstream publications. Other reliable sources include:

Questionable sources are those that have a poor reputation for checking the facts, lack meaningful editorial oversight, or have an apparent conflict of interest.

Predatory open access journals are also questionable due to the lack of effective peer-review.

Self-published and questionable sources may be used as sources of information about themselves, usually in articles about themselves or their activities, without the self-published source requirement that they are published experts in the field, so long as:

Do not reject reliable sources just because they are difficult or costly to access. Some reliable sources are not easily accessible. For example, an online source may require payment, and a print-only source may be available only through libraries. Rare historical sources may even be available only in special museum collections and archives. If you have trouble accessing a source, others may be able to do so on your behalf (see WikiProject Resource Exchange).

If you quote a non-English reliable source (whether in the main text or in a footnote), a translation into English should accompany the quote. Translations published by reliable sources are preferred over translations by Wikipedians, but translations by Wikipedians are preferred over machine translations. When using a machine translation of source material, editors should be reasonably certain that the translation is accurate and the source is appropriate. Editors should not rely upon machine translations of non-English sources in contentious articles or biographies of living people. If needed, ask an editor who can translate it for you.

Take special care with contentious material about living and recently deceased people. Unsourced or poorly sourced material that is contentious, especially text that is negative, derogatory, or potentially damaging, should be removed immediately rather than tagged or moved to the talk page.

The no original research policy (NOR) is closely related to the Verifiability policy. Among its requirements are: