Abstract: This paper presents a method to evaluate Boolean operations between free-form solids modeled using Extended Simplicial Chains (ESCs). The ESC model is a formal system to represent not only the boundary, but also the volume of free-form solids, that allows the development of simple and robust algorithms. In this implementation of the ESC model, the free-form solids and the results of the operations are bounded by PN triangles and represented by ESCs, and the surface intersection and trimming are computed using adaptive subdivision of the patches and a point in solid test specifically designed for ESCs.