I just found out that the seam book I bough actually has the answer, page314 :) Apparently I need to do some stuff in the web.xml and the faces-config. Still it worries me that jboss 4.2 breaks backwards compatibility, because some jars might or might not be in it's classpath. This means if I write a seam app now for jboss x, the sysops can't just upgrade to jboss y, without me having to adjust my seam app? Is it possible to drop the jsf implementation I want to use in my war and ignore the one that the jboss app is proposing? View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4048825#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...