Wikipedia:Using sources

It is important that sources are chosen and used properly in Wikipedia. References must be reliable sources, used in accordance with the three core content policies. For stylistic and formatting issues, please refer to Manual of Style. For the suitability of certain types of content, see What Wikipedia is not. For guidance on the encyclopedic suitability of subjects or articles as a whole, refer to Notability. For articles about living people, see Biographies of living persons.

Reliable sources
"Verifiability" requires that the facts and claims we present are verifiable by other editors. Any material that is challenged or likely to be challenged must be supported by a reliable source. "Original research" is a claim, including interpretation or analysis of facts and references, for which no reliable source can be found. Producing a reliable published source that advances the same claim taken in context is the only way to disprove original research. Citing reliable published sources is essential in our goal of building a quality reference work.

Reliable third-party sources
Reliable third-party sources should be the principal reference material for Wikipedia articles, whenever possible. These sources are up-to-date, written purposefully to inform about the subject they are being cited for, and released by a publisher with a reputation for fact-checking and accuracy. Third-party publications are preferable because they generally provide analysis, offer a more independent view and provide a broader context for the subject. Care should be taken to avoid undue weight and ensure the information cited is used in context.

Using reliable third-party sources
While articles should principally rely on reputable third-party sources, care should still be taken that the claims reported in the article are verifiable in the references cited. Claims should not rely on unclear, incongruent or passing comments, even if the source is generally reliable. Claims left open to interpretation should be precisely cited or avoided. Drawing conclusions not stated in the reference, or extrapolating a position from the claims in a source, is original research regardless of the type of source. Claims based on statements and sections from reliable sources directly dealing with the central topic of the work are preferred. It is good to report information from sections that present an extended argument with a conclusion strongly consistent with the argument. It is important that reliable references are cited in context and on topic.

Auxiliary sources
Auxiliary sources should only be used with care, or in context as used in reliable third-party sources. References from questionable, historical and "raw" sources are examples of auxiliary sources. References from the subject, or those close to the subject, are also examples of auxiliary sources. A third-party source from one article may be treated as an auxiliary source in another, because the focus has changed. Generally, any source that does not qualify as a reliable third-party source is grouped in this category. The use of these raw, first-hand, or out-of-date sources lends itself to inaccurate reporting, undue weight, and original research. Thus, they should only be used with caution and extreme care.

Using auxiliary sources
Articles should usually rely on reliable third-party sources, but there are some exceptions and occasions when auxiliary sources may prove useful. Article claims that rely on an auxiliary source should (1) only report what the source states, the accuracy of which is easily verifiable by any reasonable, educated person without specialist knowledge, and (2) make no analytic, synthetic, interpretive, explanatory, or evaluative claims. Contributors drawing on auxiliary sources should be careful to comply with both conditions. Of course, auxiliary sources may be used freely as they are used in reliable publications.

Some of these sources may be particularly reliable and helpful in presenting a complete encyclopedic article, such as census data. Some auxiliary references may also be useful for providing supporting facts, figures or limited quotations to accompany claims and analysis from reliable third-party publications. However, serious care should be taken to avoid presenting a claim or interpretation, explicit or implied, differing from the reliable references cited. Self-published and dubious sources are permitted in articles about themselves, when used with care. Editors should use discretion and consensus to identify such circumstances.