This volume contains the Proceedings of a meeting held at Montpellier from November 27th to December 1st 1989 and entitled Inverse Problems Multicen tennials Meeting . It was held in honor of two major centennials: the foundation of Montpellier University in 1289 and the French Revolution of 1789. The meet ing was one of a series of annual meetings on interdisciplinary aspects of inverse problems organized in Montpellier since 1972 and known as RCP 264 . The meeting was sponsored by the Centre National de la Recherche Scientifique (con tract GR 264) and by the Direction des Recherches et Etudes Techniques (contract 88 CO 283). The Proceedings are presented by chapters on different topics, the choice of topic often being arbitrary. The chapter titles are Tomographic Inverse Problems , Distributed Parameters Inverse Problems , Spectral Inverse Problems (Exact Methods) , Theoretical hnaging , Wave Propagation and Scattering Problems (hnaging and Numerical Methods) , Miscellaneous Problems , Inverse Methods and Applications to Nonlinear Problems . In each chapter but the first, the papers have been sorted alphabetically according to author*. In the first chapter, a set of theoretical papers is presented first, then more applied ones. There are so many well-known and excellent lectures that I will not try to refer to them all here (the reader will be easily convinced by reading the Table of Contents). My comments at the conference are summarized by the short scientific introduction at the beginning of the volume.