we apply combinatorial optimization techniques to binary mask design for optical lithography. The mask is optimized in such a way as to pre-compensate the distortions due to diffraction of the optical system. Mean squared error (MSE) criterion is used to formulate the problem as a binary linear programming (LP) one which is then solved via branch and bound and simplex algorithms. Variation of the optimal mask as a function of the optical system bandwidth is discussed. Examples involving corners squares bars and crosses are presented. 1.