Based on the work of Coons, several attempts have been made to develop programs for designing surfaces using a computer driven interactive display. However, it is considered that the problems of man-design interaction have not previously been solved successfully. In this paper techniques are developed which allow manipulation of a surface without reference to its mathematical definition and which allow modification to influence only local areas of design. Using an extension of the Coons definition a bi-quartic patch is chosen as more suitable than the bi-cubic for design. (Received December 1969)