Xquery and XSLT: an easy way to manage XML
The XSLT and XQuery standards were created by different working groups within W3C. The both share the same data model, type system and function library, and both include Xpath 2.0 as a sub language. XQuery was initially created as a query language that would work with large collections of XML documents; it can also work with individual documents. So, its capabilities overlap with XSLT, which was designed to allow input XML documents to be transformed into XML or other formats.
Anyway, there are great differences between these

