Book excerpt: The objectives of this project were to develop computer based models of soft tissues that could eventually be integrated into virtual reality-based surgical simulators. To that end, we have developed a number of computer algorithms that span the scales from the microstructural to the phenomenological, and from 1-D to 3-D. For the 1-D case, we have developed a model of fractional order viscoelasticity. For the 3-D case, we have developed an invariant-based formulation of dispersed isotropy and implemented it in a model of blood vessel. Although the later employs as statistical measure of fiber dispersion, both a essentially phenomenological models. To implement tissue microstructure, we developed a micromechanical model based on the General Method of Cells. Through this model, we were able to model fiber-matrix interactions explicitly. These models are currently being validated and implemented into larger organ simulations.