Wikipedia:Exactly one full citation

Every source (book, article, etc.) used in an article should have exactly one full citation containing all the bibliographic details of that source. Full citations are usually implemented with a citation or cite xxx template, and may be in the text (usually in a footnote created using the  tags), or collected with other full citations in a separate section (often named "References", "Sources", or "Bibliography"). These are distinct from short-cites, such as "Smith 2001", typically created with the harv family of templates, and used in-line to link to the full citation; "exactly one" does not apply to short-cites or similar links.

Sources having no full citations should be appropriately tagged, usually with citation needed or full citation needed.

Where there appears to be more than one full citation (exactly identical or not) for a given source they should be carefully examined to determine if they might be for similar but distinct sources, such as different editions of a work. (These should be cited separately, as they may differ on key details.) If so, additional information should be added to clarify the differences in the sources. Full citations differing in only the ISBN (which may reflect only the type of cover) should be merged, with the additional ISBNs appended to the citation.

Otherwise: any redundant full citations to a given source should be replaced with a short-cite, or (less satisfactory) converted to a "named-ref". The remaining full citation should be filled out as far as possible, and appropriately tagged for any missing parts; see Template:Inline cleanup tags.