XML Schema因为W3C的推荐，在2001年五月发布，是许多XML schema languages中的一支。它是首先分离于XML本身的纲要语言，故取得W3C的推荐地位。

像所有XML纲要语言一样，XML Schema有时用来表达一组纲要──一组XML文档必须遵守的规定，这样根据该纲要才『合法（Valid）』。

然而，不像大部分其他纲要语言一样，XML Schema亦意图设计来确认在一收集来的数据与内附特殊数据型别的结果，它对开发XML文档处理软件有助益，不过同时召来了非议。

An XML schema is a description of a type of XML document, typically expressed in terms of constraints on the structure and content of documents of that type, above and beyond the basic syntactical constraints imposed by XML itself. These constraints are generally expressed using some combination of grammatical rules governing the order of elements, Boolean predicates that the content must satisfy, data types governing the content of elements and attributes, and more specialized rules such as uniqueness and referential integrity constraints.