I'm creating a JAX-WS type webservice, with operations that return an object WebServiceReply. The class WebServiceReply itself contains a field of type Object. The individual operations would populate that field with a few different data-types, depending on the operation. Publishing the WSDL (I'm using Netbeans 6.7), and getting a ASP.NET application to retrieve and parse the WSDL was fine, but when I tried to call an operation, I would receive the following exception: javax.xml.ws.WebServiceException: javax.xml.bind.MarshalException - with linked exception: [javax.xml.bind.JAXBException: class [LDataObject.Patient; nor any of its super class is known to this context.] How do I mark the annotations in the DataObject.Patient class, as well as the WebServiceReply class to get it to work? I haven't been able to fine a definitive resource on marshalling based upon annotations within the target classes either, so it would be great if anybody could point me to that too. WebServiceReply.java @XmlRootElement(name="WebServiceReply") public class WebServiceReply { private Object returnedObject; private String returnedType; private String message; private String errorMessage; .......... // Getters and setters follow } DataObject.Patient.java @XmlRootElement(name="Patient") public class Patient { private int uid; private Date versionDateTime; private String name; private String identityNumber; private List<Address> addressList; private List<ContactNumber> contactNumberList; private List<Appointment> appointmentList; private List<Case> caseList; } Solution (Thanks to Gregory Mostizky for his answer) I edited the WebServiceReply class so that all the possible return objects extend from a new class ReturnValueBase, and added the annotations using @XmlSeeAlso to ReturnValueBase. JAXB worked properly after that! Nonetheless, I'm still learning about JAXB marshalling in JAX-WS, so it would be great if anyone can still post any tutorial on this. Gregory: you might want to add-on to your answer that the return objects need to sub-class from ReturnValueBase. Thanks a lot for your help! I had been going bonkers over this problem for so long!