Web Standards are the formal, non-proprietary standards and other technical specifications that define and describe aspects of the World Wide Web. In recent years, the term has been more frequently associated with the trend of endorsing a set of standardized best practices for building web sites, and a philosophy of web design and development that includes those methods.

Web standards are not fixed sets of rules, but are a constantly evolving set of finalized technical specifications of web technologies. Web standards are developed by standards organisations—groups of interested and often competing parties chartered with the task of standardization—not technologies developed and declared to be a standard by a single individual or company. It is crucial to distinguish those specifications that are under development from the ones that already reached the final development status (in case of W3C specifications, the highest maturity level).

When a web site or web page is described as complying with web standards, it usually means that the site or page has valid HTML, CSS and JavaScript. The HTML should also meet accessibility and semantic guidelines. Full standard compliance also covers proper settings for character encoding, valid RSS or valid Atom news feed, valid RDF, valid metadata, valid XML, valid object embedding, valid script embedding, browser- and resolution-independent codes, and proper server settings.