This chapter presents different algorithms for modeling soft tissue deformation in the context of surgery simulation. These algorithms make radical simplifications about tissue material property, tissue visco-elasticity and tissue anatomy. The chapter describes the principles and the components of a surgical simulator. It also presents the process of building a patient-specific hepatic surgery simulator from a set of medical images. The different stages of computation leading to the creation of a volumetric tetrahedral mesh from a medical image are especially emphasized. Later, it describes the five main hypotheses that are made in the proposed soft tissue models. Moreover, the main equations of isotropic and transversally anisotropic linear elasticity in continuum mechanics are also presented. The discretization of these equations is presented that are based on finite element modeling. The simple linear tetrahedron element is presented that provide closed form expressions of local and global stiffness matrices. After describing the types of boundary conditions existing in surgery simulation, the static and dynamic equilibrium equations in their matrix form are derived. The chapter introduces a first model of soft tissue; it is based on the off-line inversion of the stiffness matrix and can be computed very efficiently as long as no topology change is required. A second soft tissue model allows to perform cutting and tearing but with less efficiency as the previous model. A combination of the two previous models, called “hybrid model” is also presented in the chapter. It also introduces an extension of the second soft tissue model that implements large displacement elasticity.