Heterodyne techniques have proved to be a very sensitive tool for measuring minute dynamic phase changes imposed on an optical beam. In this paper, we review the application of this powerful tool to the area of micrometrology. By using a differential geometry that measures the phase difference of reflected or transmitted light from two adjacent points on a sample, it is possible to achieve a sensitivity of 0.35 A (or 0.75 X1 0-3 rad). Results of the surface studies on several samples are presented that clearly show the ability of the technique to image monomolecular layers and other minute surface perturbations.