Professor Michael is one of the leading world experts on surface integrals and the theory of measure on parametric surfaces. He is not a prolific writer, but each one of his papers is an important and deep contribution to the subject. Perhaps his most outstanding achievement is the extension of the classical Gauss-Green and Cauchy theorems to very general parametric surfaces. He made important contributions to the notion of surface area and existence of surface integrals, and proved an important conjecture of Kuratowski on the mapping of boundaries of closed subsets of the n-sphere.