I sent along a patch that does what I was talking about. As it turns out, this "does" match what C# does, i.e. I can instantiate a PropertySet from C# and it knows what to do. So this change is in keeping with your design goal. However, there are a few other problems. I will see whether I can help with these as well. 1) The Python PropertySet is exposing no methods. In ILDASM, it shows "interface PropertySet implements IPropertySet", and in C# the IPropertySet methods are available on a variable declared as PropertySet. In Python they are not. 2) The first time I try to import, it sometimes fails with an ImportError "No module named ...", but if I try again, it succeeds. It seems to have a better chance of success if I first import CLR itself. I'm not sure why that should be. Bruce