Single-sourcing is the development of information content in a form that can conveniently be the basis for other forms of content. For example, text prepared for a printed book might be prepared in a form that could also be used without additional authorial involvement or adaptation as any of: online help panels, text on a Web page in HTML, or a version of the user's guide in Portable Document Format (PDF) on a compact disc. Single-sourcing does not mean that the characteristics of different media don't need to be considered. It does mean that content can initially be entered and thereafter maintained only in one common source file or set of files. When the content needs to be presented in a particular form for a particular medium, the description of the content in the common source file enables a conversion tool to create the appropriate formatting.
Historically, the Standard Generalized Markup Language (SGML), a metalanguage, was created to enable content creators to define specific markup languages that, when used, would enable single-sourcing. Today, the Extensible Markup Language (XML) and related tools facilitate single-sourcing.
A number of content creation tools such as Framemaker include support for single-sourcing, often including the ability to convert a body of text into an HTML page or a particular kind of help file.