In computing, the term Extensible Stylesheet Language (XSL) is used to refer to a family of languages used to transform and render XML documents.

Historically, the W3C XSL Working Group produced a draft specification under the name "XSL," which eventually split into three parts:

1. XSL Transformation (XSLT): an XML language for transforming XML documents
2. XSL Formatting Objects (XSL-FO): an XML language for specifying the visual formatting of an XML document
3. XML Path Language (XPath): a non-XML language used by XSLT, and also available for use in non-XSLT contexts, for addressing the parts of an XML document.

As a result, the term "XSL" is now used with a number of different meanings:

• Sometimes it refers to XSLT: this usage is best avoided. However, "xsl" is used both as the conventional namespace prefix for the XSLT namespace, and as the conventional filename suffix for files containing XSLT stylesheet modules
• Sometimes it refers to XSL-FO: this usage can be justified by the fact that the XSL-FO specification carries the title Extensible Stylesheet Language (XSL); however, the term XSL-FO is less likely to be misunderstood
• Sometimes it refers to both languages considered together, or to the working group that develops both languages
• Sometimes, especially in the Microsoft world, it refers to a now-obsolete variant of XSLT developed and shipped by Microsoft as part of MSXML before the W3C specification was finalized

This article is concerned with the various usages of the term "XSL": for details of the various languages embraced by the term, see the relevant article.