It appears that when I put BOOST_CLASS_EXPORT_GUID in class header files, sometimes I get a Multiple definition error for the instance of the guid_initializer, if the header file is included more than once in various bits of code. If the GUID is place in the cpp file there are no problems. I can see why this happens, but the docs appear to imply I should be able to put the definition in the header files, this paragraph below (http://www.boost.org/libs/serialization/doc/serialization.html#pointero perators) "The macro BOOST_CLASS_EXPORT_GUID associates a string literal with a class. In the above example we've used a string rendering of the class name. If a object of such an "exported" class is serialized through a pointer and is otherwise unregistered, the "export" string is included in the archive. When the archive is later read, the string literal is used to find the class which should be created by the serialization library. ****This permits each class to be in a separate header file along with its string identifier****. There is no need to maintain a separate "pre-registration" of derived classes that might be serialized. This method of registration is referred to as "key export". More information on this topic is found in the section Class Traits - Export Key." Is the document misleading here, or have I missed something?? James This message (including any attachments) contains confidential and/or proprietary information intended only for the addressee. Any unauthorized disclosure, copying, distribution or reliance on the contents of this information is strictly prohibited and may constitute a violation of law. If you are not the intended recipient, please notify the sender immediately by responding to this e-mail, and delete the message from your system. If you have any questions about this e-mail please notify the sender immediately.