The eXtensible Markup Language (XML) is a universal way of structuring documents and other data.

Markup Languages have existed for many years before the start of the World Wide Web. WordPerfect and Rich Text Format (RTF) have used markup tags to provide special formatting commands that apply to specific words and text. Hyper Text Markup Language (HTML) is the markup language used for web pages. 

HTML has gained widespread use and is easy to understand. Both HTML and XML are derived from the Standard Generalized Markup Language (SGML).

1986 SGML (document markup language)

1992 HTML (web page specific markup language)

1997 XML (web page and general documents markup language)

2001 XML 1.1

Previously anyone who wanted to create web pages would have to learn HTML syntax and make the page using simple text editors.

More advanced HTML specific editors appeared that checked the web pages and HTML tags. When applications such as MS Frontpage appeared, people could author web pages without learning all the HTML tags. Many thousands of web pages were created daily, mostly showing personal homepages or company marketing information. As the use of websites became more sophisticated, the limitations of HTML as become apparent. The next section covers the similarities and differences between HTML and XML.