XML General

W3 and XML: http://www.w3.org/xml

XML Schema: http://www.w3.org/xml/schema

Microsoft: http://msdn.microsoft.com/xml/default.asp

XML in Action, William J. Pardi, Microsoft Press, 1999 (ISBN 0735605629)

XML Bible, Elliot Rusty Harold, Hungry Minds, Inc., 1999 (ISBN 0764532367)

XML Unleashed, Michael Morrison, Sams, 1999 (ISBN 0672315149)

Professional ASP XML, Mark Baartse, et al., Wrox Press, 2000 (ISBN 1861004028)

Essential XML: Beyond Markup, Don Box, et al., Addison-Wesley, 2000 (ISBN 0201709147)