The XML classes in the System.Xml namespace provide a comprehensive and integrated set of classes, allowing you to work with XML documents and data. The XML classes support parsing and writing XML, editing XML data in memory, data validation, and XSLT transformation.
Discusses the three models for processing XML data in-memory. LINQ to XML is the new model in the .NET Framework version 3.5 for processing XML data. The XmlDocument class, and its associated classes, are based on the W3C Document Object Model. The XPathDocument class is based on the XPath data model.