As Weston pointed out, there's 1001 definitions of what an ESB is, depending on your perspective. http://isp.webopedia.com/TERM/E/ESB.html[/url] is fairly typical, as is [url]http://en.wikipedia.org/wiki/Enterprise_service_bus. Some bundle orchestration, application servers etc. as part of the ESB. The definition we've been working towards is that the ESB is concerned with message routing and service/transport plugins: all of the capabilities you've expect from a "classic" ESB can be cast in those terms. Very similar to Weston's the PCI/CPU bus analogy. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4038121#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...