Grid generation is concerned with discretizing surfaces and volumes in 3D space. The original surfaces defining a geometry might be given as a finite set of triangles/quadrilaterals (discrete form) or as parametrically defined surfaces (analytical form). A new interactive technique is presented for computing a B-spline approximation for geometries given in either form. The method requires user interaction for the selection of subsets of the given surfaces to be approximated. Once all subsets of surfaces have been approximated by B-spline surfaces, these are united yielding an overall C2 continuous approximation.