XHTML

Marking up documents in XHTML
The HTML Writers Guild article, detailing the main differences between HTML and XHTML.
http://gutenberg.hwg.org/markupXHTML.html

New Architect
Article exploring the issues involved in migrating from HTML to XML.
http://www.ddj.com/architect/184413727

NYPL Styleguide
XHTML 1.0 overview. Includes discussion of accessibility and document validation. Also XHTML authoring tips and tools featuring the use of Dreamweaver.
http://www.nypl.org/styleguide/xhtml/

XDG: XHTML Design Guide
Introduction, tutorial, standards documents, and links to articles.
http://www.onaicul.com/xdg.html

XHTML :: How to succeed
Tips and caveats on HTML to XHTML migration for existing browsers.
http://ptaff.ca/xhtml/?lang=en_CA

XHTML is the Most Important XML Vocabulary
An article covering possible future outcomes for version 2 of the standard.
http://www.xml.com/pub/a/2003/05/21/deviant.html

XHTML Reference
An XHTML reference with articles describing HTML-compatibility.
http://xhtml.com/

XHTML Web Design for Beginners
An introductory article for those with no prior experience of HTML. Covers version 1.0 Transitional.
http://www.miswebdesign.com/resources/articles/web-design-xhtml-1-1.html

XHTML: Where XML and HTML meet
Discussion of XHTML 1.0 and how it improves on the HTML 4.0 standard. Examines the issues involved in the transition between HTML and XHTML. Also explores backwards compatibility to HTML and XHTML modularization.
http://www.webreference.com/xml/column6/