• 1998: W3C defined XML as a modern replacement for SGML
• XML stands for Extensible Markup Language
• To allow a wide range of data and information to be represented as Web documents

<Employee>
     <Name>
          <Surname>Matthews</Surname>
          <Firstname>Brian</Firstname> 
     </Name>
     <Title>Dr.</Title>
     <Area>e-Science Systems Research</Area>
     <Dept>e-Science Centre</Dept>
     <Lab>Rutherford Appleton Laboratory<Lab>
     <Email>brian.matthews@stfc.ac.uk</Email>
     <Tel code="RAL">6648</Tel>
     <Fax code="RAL">5831</Fax>
</Employee>

• Elements must be well formed, correctly nested
• All attributes must be in quotes
• There is a single root element
• Example languages are MathML, SMIL, XSLT, SVG, XForms and, of course, XHTML