Robert, A comment in interface_oarchive.hpp states that interface_oarchive<Archive>::This() is supposed to return the a pointer to the most derived class. Actually, it gives you a pointer to the "Archive" template parameter which may or may not be the most derived class, depending on how your internal "invoke" plumbing resolves the type. In the following case I was able to get the most derived class only by overriding both operator<<(const T & t) and save_override()(using VC2k3): class fau_xml_woarchive : public boost::archive::xml_woarchive { public: [...] template<class T> void save_override(const ::boost::serialization::nvp<T> & t, int i) { save_start(t.name()); boost::archive::save(*this, t.value()); save_end(t.name()); } template<class T> _Mytype& operator<<(const T & t) { save_override(t, 0); return *this; } [...] }; Was that your intention? Regards, George.