Alista Part
A List Apart Magazine (ISSN: 1534-0295) explores the design, development, and meaning of web content, with a special focus on web standards and best practices.
http://www.alistapart.com/articles/hellxml

W3 Schools
Free HTML XHTML CSS JavaScript DHTML XML DOM XSL XSLT RSS AJAX ASP ADO PHP SQL tutorials, references, examples for web building.
http://www.w3schools.com/xml/default.asp

Wdvl
This XML introduction is geared toward newcomers who have heard the buzz, but don't know what all the fuss is about. The article briefly surveys a number of new Web technologies such as XLL, XSL, RDF, DOM, MathML, SMIL, PGML, and how they relate to XML. Benefits of XML are stressed, as are potential applications in diverse fields. A reference section provides links to key XML resources, as well as to collections of other introductory articles.
http://www.wdvl.com/Authoring/Languages/XML/Intro/

Skew
This is a crash course in some essential concepts for software developers who are reading and writing XML documents on a regular basis. It is oriented toward people with some sort of programming background. The intended audience should already understand some basic things like what bits and bytes are, how to read hexadecimal numbers, what characters are, and they should be comfortable with phrases like "hierarchical data model".
http://skew.org/xml/tutorial/

MSDN
XML has become the almost universally supported way of exchanging documents and data across applications and platforms. Microsoft was a pioneer in XML development and takes pride in the quality, performance, and standards conformance of our XML technologies. We have a family of XML technologies that allows users with differing requirements to do what they need to do, as simply and efficiently as possible.
http://msdn.microsoft.com/en-us/xml/default.aspx

XML Cover Pages
The Cover Pages is a comprehensive, online reference collection supporting the XML family of markup language standards, XML vocabularies, and related structured information standards. Edited by Robin Cover since 1986, this public access knowledgebase promotes and enables the use of open, interoperable, standards-based solutions which protect digital information and enhance the quality of data processing.
http://xml.coverpages.org/xml.html

XML Silmaril
This is the list of Frequently-Asked Questions about the Extensible Markup Language (XML). It has answers to most of the common questions people ask about XML. If you are seeking answers to questions about related areas such as HTML, SGML, CGI scripts, PHP, JSP, Java, databases, or penguins, you may find some pointers, but you should probably look elsewhere as well.
http://xml.silmaril.ie/

Oracle
Whether you are a beginner, intermediate, or advanced XML user, the XML Technology Center provides you up-to-date content and guidance to develop all types of XML-based applications.
http://www.oracle.com/technology/tech/xml/index.html

15 Seconds
With the advent of the Web, many organizations have put large amounts of information in the form of HTML pages. These pages are tied up to a single presentation. Extensible Markup Language (XML) allows us to separate the content and the presentation. If the developers think of a migration of these HTML pages to XML mechanically -- trying to create well-formed documents out of the existing HTML documents, or cutting and pasting contents from HTML to the newly created XML files, or whatever -- that would be a pretty daunting task. This article shows how the tool HTML Tidy and a COM Wrapper can make our job simpler.
http://www.15seconds.com/Issue/010601.htm

Tizag
XML is a markup language. The mighty ones who created this acronym cheated a little, as XML stands for eXtensible Markup Language. XML was released in the late 90's and has since received a great amount of hype. The XML standard was created by W3C to provide an easy to use and standardized way to store self-describing data (self-describing data is data that describes both its content and its structure).
http://www.tizag.com/xmlTutorial/index.php

XML Files
Need an introduction to XML? Learn what XML is all about and discover how XML differs from HTML. Explore XML syntax rules, learn how to write well-formed XML documents, adjust XML attributes, validate XML documents, and more.
http://xmlfiles.com/xml/

Stylus Studio
Browse our selection of XML tutorials covering topics including Data Integration, XQuery, XML Schema, and specific Stylus Studio operations. You'll find XML tutorials and tips for troubleshooting some of the most common Stylus Studio technical support issues, and for tackling more advanced XML development issues.
http://www.stylusstudio.com/xml_tutorial.html

XML
We've expanded our XML news coverage and improved our search! Search for all things XML across O'Reilly!
http://www.xml.com/index.csp