Here, the state-of-the-art is presented with respect to analytical and design methods incorporating uncertainty in the geologic environment. Particular emphasis is placed on practical applications where quantifying uncertainty and risk associated with the geologic environment plays an important, if not dominant, role in analysis and design. The role of uncertainty in the geologic environment is illustrated through numerous examples involving field data as well as several case histories. Quantitative assessments of uncertainty in the geologic environment are illustrated for site chartacterization, variability in soil and rock properties, dams and stability, earth structures and foundations, geoenvironmental applications, and seismic assessment and dynamics. The application of models for analyzing uncertainty in the geologic environment also is presented.