Extensible Stylesheet Language Transformations, or XSLT, is an XML-based formal language used for the transformation of XML-documents. The original document is not changed; rather, a new document is created based on the content of an existing one. The new document may be serialized (output) by the processor in standard XML syntax or in another format, such as HTML or plain text. XSLT is most often used to convert data between different XML schemas or to convert XML data into web pages or PDF documents.
XSLT was produced as a result of the XSL development effort within W3C during 1998–1999, which also produced XSL Formatting Objects (XSL-FO) and the XML Path Language, XPath. The editor of the first version (and in effect the chief designer of the language) was James Clark. The version most widely used today is XSLT 1.0, which was published as a Recommendation by the W3C on 16 November 1999. A greatly expanded version 2.0, under the editorship of Michael Kay, reached the status of a Candidate Recommendation from W3C on 3 November 2005.