Learn XSLT XQuery

Specifications

XSL Transformations (XSL) Version 2.0: This is the main guide to the XSLT 2.0 language.
XQuery 1.0: An XML Query Language [Errata]: This is the main guide to the XQuery 1.0 language.
XQuery 3.0: An XML Query Language: This is the main guide to the XQuery 3.0 language.
XQuery 1.0 and XPath 2.0 Functions and Operators [Errata]: This documents the standard XQuery 1.0 library functions.
XPath and XQuery Functions and Operators 3.0: This documents the standard XQuery 3.0 library functions.
XQuery 1.0 and XPath 2.0 Data Model (XDM) [Errata]: This describes the data model and type system which underpin the family of languages which operate on it.
XQuery and XPath Data Model 3.0: This describes the updated data model and type system for XQuery 3.0 and XPath 3.0.
XSLT 2.0 and XQuery 1.0 Serialization [Errata]: XQuery is a language for returning XDM values. Serialization is about the representation of those values as XML, XHTML, HTML or text.
XSLT and XQuery Serialization 3.0: Version 3.0 adds support for HTML 5.
XQuery 1.0 and XPath 2.0 Formal Semantics [Errata]: This technical document is invaluable to implementors of XQuery.
XML Syntax for XQuery 1.0 (XQueryX) [Errata]: It's certainly not pretty, but the XML Syntax is useful when creating and modifying queries programmatically..
XQueryX 3.0: An updated XQueryX for the new language features of XQuery 3.0.

W3C XML Query (XQuery): The home of XQuery at the World Wide Web Consortium.
XQuery talk: A popular XQuery mailing list frequented by users and developers.
FunctX XQuery Functions: A large collection of XQuery functions.
xqdoc: A documentation tool for XQuery libraries.
XQuery: O'Reilly Media, Inc.
XQuery from the Experts: A Guide to the W3C XML Query Language: Addison-Wesley Professional.
Querying XML: XQuery, XPath, and SQL/XML in context: Morgan Kaufmann.