[Drools 5.5.0 Final] Hey, for using the marshaller I needed to add ProtoBuf jars to my project like this: <!-- Protobuf (!important: v2.4.1) for marshalling drools knowledge sessions --> <dependency> <groupId>com.google.protobuf</groupId> <artifactId>protobuf-java</artifactId> <version>2.4.1</version> </dependency> Is there any particular reason why it is not included in the drools jars or at least mentioned in the documentation? Apparently drools (5.5) only works with v2.4.1 and not with the new v2.5 of ProtoBuf - Alex