« Environmental Geomechanics » is a relatively new discipline at the interface between built and natural environment. It is devoted to the understanding of the mechanical behavior of geomaterials (mainly soil and rock but also concrete and others) under various environmental conditions. The new theories and models developed in this context will find applications in a large field of engineering (waste disposal, underground structures, agriculture, natural disasters, energy production, depollution, etc.). Complexity is an important feature of Environmental Geomechanics: it concerns the mixture of several species and phases, complicated interactions between constituents, and highly nonlinear behavior. As a consequence, experimental evidence is difficult to obtain and laboratory as well as in situ testing procedures present serious challenges. Further, advanced numerical techniques are required to solve the complex nonlinear analytical equation systems. Finally, integration of new models for engineering applications will require a considerable effort amongst engineering teams (and a clear need for advanced education in this field). An interdisciplinary approach will be the key issue for a rapid development of Environmental Geomechanics. This is what we have tried to achieve by inviting to Monte Verità (the Mountain of Truth) researchers from various fields and educational backgrounds: Soil Physics, Mineralogy, Soil and Rock Mechanics, Chemistry, Biology and Applied Mathematics. With their help, we were able to edit the present volume that we think will be of interest to many in this growing scientific community. The first part of the volume contains invited keynote lectures addressing various aspects of Environmental Geomechanics. It could serve as a starting point for further research thanks to its in-depth treatment and its rich bibliographic references. The second part contains various shorter selected contributions. Each of them reflect the broad scope of Environmental Geomechanics and an appeal for more research efforts in this field. Many practical problems relating to engineering practice are also presented which make the book an invaluable “state of the art” guide in this very important field. The Editors L. Vulliet, L. Laloui & B. Schrefler Lausanne, May 29, 2002.