Computer methods are in the forefront of the procedures for analysis and design for geotechnical problems. Constitutive models that characterize the behavior of geologic materials and interfaces / joints play a vital role in the solutions obtained by using computer methods or any other solution procedure. The literature on both constitutive and computer models is wide; attention in this paper is devoted to the disturbed state concept (DSC) for constitutive modeling and the finite element method for computer solutions. The disturbed state concept, a unified and hierarchical approach, provides a unified framework for characterization of the behavior of geologic materials and interfaces / joints. Important factors such as elastic, plastic and creep responses, stress paths, volume change (contraction and dilation), disturbance (softening and damage or stiffening), thermal effects, partial saturation and liquefaction can be included in the same DSC framework. Because of its hierarchical nature, simplified models for specific applications can be derived from the DSC. It has been applied successfully for defining behavior of many geologic materials and interfaces/joints.