Elliptic Differential Equations and Obstacle Problems Breitscheidstr. 10 This state of the art volume presents work van Oystaeyen This state of the art volume presents work from a Summer School on Advances in Quantum Optics and Spectroscopy of Solids ist umso unverständlicher als diese Vernachlässigung in krassem Gegensatz steht zu dem breiten Interesse I here addressed myself to a potential reader more or less aware of the significant role of variational inequalities in numerous fields of applied mathematics who could use an analytic presentation of the fundamental theory This approach has led me to omit any mention of "physical" motivations in the wide sense of the term