XML (eXtensible markup language) is the newest markup standard for the Internet - it is the new HTML. XHTML is a language that uses the vocabulary of HTML and the syntax of XML, and as such makes the best of both worlds. It allows you to markup pages with the simplicity of HTML, but has additional power, because it is extensible, which means that you can create your own tags. As we move forward to a world where we can access the Internet via devices other than the browser, XHTML will become increasingly important, allowing you to write the same content once, which can then be viewed in a variety of ways.