When lawyers present legal arguments and judges write opinions, they cite authority. They lace their representations of what the law is and how it applies to a given situation with references to statutes, regulations, and prior appellate decisions they believe to be pertinent and supporting. They also refer to persuasive secondary literature such as treatises, restatements, and journal articles. As a consequence, those who would read law writing and do law writing must master a new, technical language – "legal citation."

For many years, the authoritative reference work on "legal citation" was a manual written and published by a small group of law reviews. Known by the color of its cover, The Bluebook was the codification of professional norms that introduced generations of law students to "legal citation." So completely do many academics, lawyers, and judges identify the process with that book they may refer to putting citations in proper form as "Bluebooking" or ask a law student or graduate whether she knows how to "Bluebook." The most recent edition of The Bluebook: A Uniform System of Citation, the nineteenth, was published in 2010. In 2000 a competing reference appeared, one designed specifically for instructional use. Prepared by the Association of Legal Writing Directors, the ALWD Citation Manual: A Professional System of Citation (4th ed. 2010) has won wide acceptance in law schools.

Differences between the two are minor (and noted here). In the way that dictionaries both prescribe and reflect usage, so do these manuals. Both also reflect the environment of their creation – law schools with comprehensive print libraries and full access to the major commercial online legal information systems. The realities of professional practice in many settings, particularly at a time when digital distribution of legal materials is displacing print, lead to dialects or usages in legal citation neither manual includes.

This introduction to legal citation is focused on the forms of citation used in professional practice rather than those used in journal publication. For that reason, it does not cover The Bluebook's distinct typography rules for the latter. Furthermore, it aims to identify the more important points on which there is divergence between the rules set out in the two manuals and evolving usage reflected in legal memoranda and briefs prepared by practicing lawyers.

Like other new languages, "legal citation" is easier to read than it is to write, at least at first. The active use of any language requires greater mastery than the receiving and understanding of it. In addition, there is the potential confusion of dialects or other nonstandard forms of expression. As already noted, "legal citation," like other languages, does indeed have dialects. Most are readily understandable and thus pose little likelihood of confusion for a reader. To the beginning writer, however, they present a serious risk of misleading and inconsistent models. As a writer of "legal citation," you must take care that you check all references that you find in the work of others. This includes citations in court opinions. Commercial publishers have long viewed citation as a subtle form of advertising through branding. Thus, citations in decisions published in the multiple series of the National Reporter System of the Thomson Reuters unit known as West (from the Atlantic Reporter to the Federal Supplement) have been altered by its editors to refer to other West publications. In addition, several important state courts, California and New York among them, have idiosyncratic citation norms for their own decisions. Many more cite their state's statutes and administrative regulations without repetition of a full abbreviation of the state's name in each reference, that being implied by context. While each of these courts is likely to accept – indeed, may even prefer – briefs using the same citation dialect, Federal courts in the same state may not. In short, copying and pasting citations from decisions and other references into one's own writing is almost certain to yield inconsistent, nonstandard, and even incomplete citations.