Polyhedra constitute a very powerful tool to model scenes in image syn thesis and Computer Aided Design Generalized polyhedra are standard poly hedra with non planar surfaces They are introduced in this paper to allow combining features of Boundary Representation modelling and of Free Form Surface modelling Composing these two approaches is not that simple and it is hoped that object oriented environment can help things a little This paper analyses the use of an object oriented methodology to help combine two major modelling techniques and tries to demonstrate the relevance of such schemes