First of all, you should realize that XML isn’t much use without its two close companions XPath and XSLT. There are more XML-related markup languages, and they’re useful too, but I’d start with XML, XPath and XSLT.

The best way to start learning is online and free! Visit W3 Schools and you’ll see the links to tutorials for XML, XPath, XSLT and more down the left side. I build applications with XML, and from time to time, I still refer to the tutorials there.

The only book I use on a regular basis is XSLT by Doug Tidwell, published by O’Reilly. I use that regularly, though. It’s well worth the purchase.

Once you know the basics of XML, XPath and XSLT, and assuming you already know some basic HTML, all you need is a simple text editor like Notepad and any web browser to display XML data the way you want it on a web page.

After that, when you want to get fancier, you’ll have to learn the XML classes for whatever web scripting you want to use—PHP, Java or .NET. I use .NET and like it a lot. I bought quite a few books on XML and .NET, and they were all horrible. I just use the MSDN documentation.