The solution of stress analysis problems through numerical, computer oriented techniques is becoming more and more popular in soil and rock engineering. This is due to the ability of these methods to handle geometrically complex problems even in the presence of highly nonlinear material behaviour, characterizing the majority of soils and rocks, and of media consisting of two or more phases, like saturated and partially saturated soils. Aim of this book is to present to researchers and engineers working in the various branches of geomechanics an updated state of the research on the development and application of numerical methods in geotechnical and foundation engineering. Particular attention is devoted to the formulation of nonlinear material models and to their use for the analysis of complex engineering problems. In addition to the constitutive modelling, other topics discussed concern the use of the finite element and boundary element methods in geomechanics; the dynamic analysis of inelastic and saturated soils; the solution of seepage, consolidation and coupled problems; the analysis of soil-structure interaction problems; the numerical procedures for the interpretation of field measurements; the analysis of tunnels and underground openings.