No synchronization is needed to call newStatelessKnowledgeSession. I'm unclear on what you mean by "work with" the stateless session. While it's running the execute method no outside initiated threads should be interacting with the session. If outside threads will be initiating interaction you probably should be using a stateful session. Stateless sessions generally follow this pattern: StatelessKnowledgeSession session = <make the session> session.execute(<all of your data>); //blocking call ...do something with the results... Outside threads shouldn't initiate contact while the blocking call above is processing. If you do, use the execute(Command) method, which are thread safe, but that's not really the use case for a stateless session. --- On Tue, 11/3/09, Laird Nelson <ljnelson(a)gmail.com&gt; wrote: