extern "C" Interface* DLLCreate() { return new InterfaceImpl; }

extern "C" void DLLDestroy( Interface* p ) { delete p; }

and then construct an InterfacePtr( DLLCreate(), DLLDestroy ). You'll need a public virtual destructor in this case, though.

I changed to this: void DLLCreate( Interface& rInterface ) { // Implementation option #1: rInterface.reset( new InterfaceImple ); // Implementation option #2: rInterface = InterfacePtr( new InterfaceImpl ); } Is this a valid solution as well? At least it compiles - but with the first solution I have the feeling that I could run into the boundary problem, since the actual pointer is not constructed on the DLL side. But as I said - I can only guess here... Is there a difference between both solutions?

Yes, it's allowed. Since you are using the DLL runtime, you probably don't need to interoperate with different C++ compilers so you probably need to just omit the extern "C" from DLLCreate. But how can I load the function than after it got mangled?