A style guide is a set of standards for the writing and design of documents, either for general use or for a specific publication, organization, or field. A style guide establishes and enforces style to improve communication. To do that, it ensures consistency (within a document and across multiple documents) and enforces best practice in usage and in language composition, visual composition, orthography (including spelling, capitalization, hyphenation, and other punctuation), and typography.
For academic and technical documents, a guide may also enforce best practice in ethics (such as authorship, research ethics, and disclosure), pedagogy (such as exposition and clarity), and compliance (technical and regulatory). Style guides are common for general and specialized use, for the general reading and writing audience, and for students and scholars of various academic disciplines, medicine, journalism, the law, government, business, and specific industries.
Style guides vary widely in scope and size. A comprehensive guide tends to be long and is often called a style manual or a manual of style (MOS or MoS). A short style guide is often called a style sheet. (The words manual and sheet thus connote long and short guides, respectively.)
The variety in scope and length is enabled by the cascading of one style over another, in a way analogous to how styles cascade in web development and in desktop publishing (for example, how inline styles in HTML cascade over CSS styles). Each project (such as one book, journal, or monograph series) typically has a short style sheet that cascades over the somewhat larger style guide of an organization (such as a publishing company), whose content is usually called house style.
Most house styles, in turn, cascade over an industry-wide or profession-wide style manual that is even more comprehensive—large enough in scope and length to be a reference work in the form of a website (online) or a book (print).
Examples of the latter include:
- Oxford style and Chicago style for general publishing and readership
- USGPO style or AGPS style for government publications
- AP style for journalism
- APA style and ASA style for the social sciences
- CSE style for various physical sciences
- ACS style for chemistry
- AMA style for medicine
- Bluebook style for law
Finally, these reference works cascade over the orthographic norms of each language (such as English orthography), which may be subject to national variety (such as the different tendencies of American English and British English) and, for some standard languages, a language academy.
Guides in specific scientific and technical fields cover nomenclature, which specifies names or classifying labels that are preferred because they are clear, standardized, and ontologically sound (e.g., taxonomy, chemical nomenclature, and gene nomenclature).
Most style guides are revised periodically to accommodate changes in conventions and usage. The frequency of updating and revision control are determined by the subject matter. For style manuals in reference work format, new editions typically appear every 1 to 20 years. For example, the AP Stylebook is revised annually.
Many house styles and individual project styles change more frequently, especially for new projects, and version dates, notifications to users, or both are often used.