The Extensible Messaging and Presence Protocol (XMPP) is an open technology for real-time communication, which powers a wide range of applications including instant messaging, presence, multi-party chat, voice and video calls, collaboration, lightweight middleware, content syndication, and generalized routing of XML data. The technology pages provide more information about the various XMPP “building blocks”. Several books about Jabber/XMPP technologies are available, as well.
The core technology behind XMPP was invented by Jeremie Miller in 1998, refined in the Jabber open-source community in 1999 and 2000, and formalized by the IETF in 2002 and 2003, resulting in publication of the XMPP RFCs in 2004 and updated RFCs in 2011 (see the history page for more details).
Although the core technology is stable, the XMPP community continues to define various XMPP extensions through an open standards process run by the XMPP Standards Foundation. There is also an active community of open-source and commercial developers, who produce a wide variety of XMPP-based software.
If you have any questions about the use or development of XMPP technologies, feel free to participate in one of the open discussion venues hosted by the XMPP Standards Foundation.