Hi, I am using Drools 5.1.1 and I have the impression that the WorkingMemoryEventListener is not called when using a StatelessKnowledgeSession configured in Sequential mode. Does anyone have experienced such a behavior? When using the SequentialOption.NO option, the little program below (in PS) displays: Retracting: to-be-removed Retracted: to-be-removed When using the SequentialOption.YES option, the program displays: Retracting: to-be-removed Many thanks in advance, Bruno. PS : Here is the sample code // DRL: rule "Retract to-be-removed string" when $s : String(this == "to-be-removed") then System.out.println("Retracting: " + $s); retract($s); end // listener: public class MyListener implements org.drools.event.rule.WorkingMemoryEventListener { public void objectInserted( org.drools.event.rule.ObjectInsertedEvent event) { } public void objectRetracted(org.drools.event.rule.ObjectRetractedEvent event) { System.out.println("Retracted: " + event.getOldObject().toString()); } public void objectUpdated(org.drools.event.rule.ObjectUpdatedEvent event) { } } // main: KnowledgeBuilder builder = KnowledgeBuilderFactory.newKnowledgeBuilder(); builder.add(ResourceFactory.newFileResource(new File("simpleRule.drl")),ResourceType.DRL); KnowledgeBaseConfiguration configuration = KnowledgeBaseFactory.newKnowledgeBaseConfiguration(); configuration.setOption(SequentialOption.YES); // change this line to change the program behavior KnowledgeBase knowledgeBase = KnowledgeBaseFactory.newKnowledgeBase(configuration); knowledgeBase.addKnowledgePackages(builder.getKnowledgePackages()); StatelessKnowledgeSession session = knowledgeBase.newStatelessKnowledgeSession(); MyListener handler = new MyListener(); List<Command<?>> commands = new ArrayList<Command<?>>(); commands.add(CommandFactory.newInsert("to-be-removed")); commands.add(new AddEventListenerCommand(handler)); session.execute(CommandFactory.newBatchExecution(commands));