Elizabeth Shown Mills, Evidence Explained: Citing History Sources from Artifacts to Cyberspace, rev. ed. (Baltimore: Genealogical Publishing Co., 2009) takes an in-depth look at genealogical sources; it incorporates a citation style. Although the sources and other aspects of the style are US centric, the analytical principles are universal. Because of its US focus, it might be better to suggest Evidence Explained is the closest thing genealogists have to a de facto standard.
As ACProctor explained, Evidence Explained is itself an extension of The Chicago Manual of Style (CMOS). Comments that follow are intended to put this in context and provide more insight, especially about UK practices.
The best known citation guides are a part of style guides, that set out standards for consistency/uniformity in the writing process. This consistency aids in readability. To get a feel for the broad range of topics covered by a comprehensive style guide, glance over the CMOS topical online Q&A index. Creating/maintaining a comprehensive style guide like CMOS no doubt requires substantial resources.
Style guides/manuals are essentially writing guides; they are commonly language specific. ACProctor mentioned some comprehensive styles that are both long standing and widely used. The Wikipedia entry, "Style guide," includes a list, too. Given ColeValleyGirl's UK interest, she may want to review Hart's Rules/Oxford (or New Oxford) Guide to Style or The Complete Guide to Referencing and Avoiding Plagiarism.1
Across all disciplines, there are thousands of publishers, educators and others who develop submission guidelines that incorporate stylistic preferences. Sometimes the guidelines specify the use of a third party style, like CMOS, APA, etc. Frequently, however, the guidelines are based on a more comprehensive style and then modified slightly. Guides associated with a specific organization or publication are called "house styles" or "editors styles." From among the great variety of house styles, many in the US could be described as "APA with a few twists" or "CMOS, with a few twists," etc.
Scholarly genealogical journals have established submission guidelines. Examples follow for a few US based journals.
The best way to learn the styles used by the journals, The Register, The Quarterly and The Record, is to read current issues. All three editors generally follow Chicago Manual of Style ... with some twists. More information is available about the genealogical journals and submission standards at the end of this article.
Citation styles have readability objectives, and stylistic formatting serves as a sort of shorthand. Many different terms are used to describe citation styles generally---author date, note, etc. Disciplines tend to approach citations differently, and the options favored by some areas of study are greatly abbreviated when compared the note or numbered systems genealogists favor.
- author date, in-line system (example): (Titus 1963) or (Titus 1963, 73)
- note/number system citation (example): 1. Warren Irving Titus, Winston Churchill (New York: Twayne Publishers, 1963), p. 73.
While most disciplines work with a range of published materials, genealogists (and historians) work extensively with unpublished and archival materials. Archives favor sometimes complex hierarchical organization schemes. Many archives publish their own citation guides as an aid to researchers.
Of general note, UK archives favor citations that work from the largest to the smallest element in the hierarchy. Archives in the United States tend to reverse the order (thus US note style citations tend to work from the smallest element to the largest). Separate from this large-to-small or small-to-large arrangement, variances in language and grammar between the US and UK create other differences between UK and US citations.
Other genealogy style guide materials:
- Michael Leclerc and Henry Hoff, editors, Genealogical Writing in the 21st Century: A Guide to Register Style and More, 2nd ed. (Boston, Mass.: New England Historic Genealogical Society, 2006).
- Helen Schatvet Ullmann, CG, FASG (New England Historic Genealogical Society) "Register Style Template."
- Joan F. Curran, Madilyn C. Crane, and John H. Wray, edited by Elizabeth Shown Mills, Numbering Your Genealogy: Basic Systems, Complex Families, and International Kin, rev. ed. (Washington: NGS, 2008).
- Board for Certification of Genealogists, The BCG Genealogical Standards Manual (Orem, Utah: Ancestry Publishing, 2000).
1 Reference only: Scribd The Oxford Guide to Style