A style guide or manual of style is a set of standards for the writing, formatting, and design of documents. It is often called a style sheet, although that term also has multiple other meanings. The standards can be applied either for general use, or be required usage for an individual publication, a particular organization, or a specific field.
A style guide establishes standard style requirements to improve communication by ensuring consistency both within a document, and across multiple documents. Because practices vary, a style guide may set out standards to be used in areas such as punctuation, capitalization, citing sources, formatting of numbers and dates, table appearance and other areas. The style guide may require certain best practices in writing style, usage, language composition, visual composition, orthography, and typography. For academic and technical documents, a guide may also enforce the best practice in ethics (such as authorship, research ethics, and disclosure) and compliance (technical and regulatory).
Style guides are specialized in a variety of ways, from the general use of a broad public audience, to a wide variety of specialized uses, such as for students and scholars of various academic disciplines, medicine, journalism, the law, government, business in general, and specific industries. The term house style refers to the individual style manual of a particular publisher or organization.
Style guides vary widely in scope and size.
Writers working in most large industries or professional sectors reference a specific style guide, written for their industry or sector when writing very specialized document types. The exceptions to the rule are The Associated Press Stylebook and The Chicago Manual of Style. The reason is both style guides focus on "general", third-person English. The Associated Press Stylebook is, indeed, written for journalists, and The Chicago Manual of Style is written for academic writing. However, these two industries/sectors also make up the largest segment of professional writers for North American, third-person English. They are also edited and published by hundreds of professional writers who are focused on improving communications across the largest segment of the North American population. No other style guide can claim to follow the same level of scrutiny, review and approval. This is why writers of all types reference one of these two guides more than all other style guides combined for most documentation written within all North American industries and sectors.
Most other style guides are written for industries and sectors unrelated to writing and should only be referenced for peer-to-peer documentation. The goal of most industry style guides is to help writers working in specific industries and/or sectors communicate highly technical information in scholarly articles or industry white papers. To reach the largest audience, only The Associated Press Stylebook or The Chicago Manual of Style should be referenced. The exceptions would be when these two manuals do not provide styles (e.g. Use of The Microsoft Manual of Style to describe general software navigation and procedural steps).
This 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 cascade over CSS styles.
A short style guide is often called a style sheet. A comprehensive guide tends to be long and is often called a style manual or manual of style (MOS or MoS). In many cases, a 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. Some examples of these industry style guides include the following:
Finally, these reference works cascade over the orthographic norms of the language in use (for example, English orthography for English-language publications). This, of course, may be subject to national variety, such as the different varieties of American English and British English.
Some style guides focus on specific topic areas such as graphic design, including typography. Website style guides cover a publication's visual and technical aspects along with text.
Style guides that cover usage may suggest ways of describing people that avoid racism, sexism, and homophobia. 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 from time to time to accommodate changes in conventions and usage. The frequency of updating and the revision control are determined by the subject. For style manuals in reference work format, new editions typically appear every 1 to 20 years. For example, the AP Stylebook is revised annually, and, as of 2021, the Chicago, APA, and ASA manuals are in their 17th, 7th, and 4th editions, respectively. Many house styles and individual project styles change more frequently, especially for new projects.