In certain jurisdictions, including the United Kingdom and other Westminster-influenced jurisdictions (such as Canada or Australia), as well as the United States and the Philippines, primary legislation has both a short title and a long title.

The long title (properly, the title in some jurisdictions) is the formal title appearing at the head of a statute (such as an act of Parliament or of Congress) or other legislative instrument. The long title is intended to provide a summarised description of the purpose or scope of the instrument. Like other descriptive components of an act (such as the preamble, section headings, side notes, and short title), the long title seldom affects the operative provisions of an act, except where the operative provisions are unclear or ambiguous and the long title provides a clear statement of the legislature's intention.

The short title is the formal name by which legislation may by law be cited. It contrasts with the long title which, while usually being more fully descriptive of the legislation's purpose and effects, is generally too unwieldy for most uses. For example, the short title House of Lords Act 1999 contrasts with the long title An Act to restrict membership of the House of Lords by virtue of a hereditary peerage; to make related provision about disqualifications for voting at elections to, and for membership of, the House of Commons; and for connected purposes.

In the United Kingdom, the long title is important since, under the procedures of Parliament, a bill cannot be amended to go outside the scope of its long title. For that reason, modern long titles tend to be rather vague, ending with the formulation "and for connected purposes". The long title of an older act is sometimes termed its rubric, because it was sometimes printed in red.^{[citation needed]}

Short titles for acts of Parliament were not introduced until the mid-19th century, and were not provided for every act passed until late in the century; as such, the long title was used to identify the act. Short titles were subsequently given to many unrepealed acts at later dates; for example, the Bill of Rights, an act of 1689, was given that short title by the Short Titles Act 1896, having until then been formally referred to only by its long title, An Act Declaring the Rights and Liberties of the Subject and Settling the Succession of the Crown. Similarly, in the US, the Judiciary Act of 1789, which was ruled unconstitutional in part by Marbury v. Madison (1803), was called "An Act to establish the Judicial Courts of the United States".

The long title was traditionally followed by the preamble, an optional part of an act setting out a number of preliminary statements of facts similar to recitals, each starting Whereas...

Unlike the long title, which precedes the preamble and enacting formula, and thus sits outside the main body of text, the short title for modern legislation is explicitly defined by a specific section, typically at the very end or very beginning of the main text. As with the above example, short titles are generally made up of just a few words that describe in broad terms the area of law being changed or the thing affected, followed by the word "Act" and then the year in which the legislation is formally enacted. Occasionally, the word "Act" may be replaced with another descriptor. Common examples are "Code" and "Charter".

A notable exception is Israel, in which this convention is reversed. The short title sits outside the main body of legislation, and the summary description of the law, which is made optional, is defined by a specific section if existing. For example, the Combating Iran's Nuclear Program Act, which under the usual convention would have begun with the long title