The work presented in this manuscript is focused on the modeling and simulation of soft tissue. I proposed an original discrete biomechanical model which is able to simulate interactions between biological or medical objects. I also developed a software environment, including two XML languages and a toolkit, in order to build a framework for comparing and validating physical models. This environment was used to compare my model with other approaches. The proposed model was applied in different clinical and biological domains. In Computer Assisted Medical Intervention, the model is used to help the surgeon or clinician in the diagnosis stage (respiratory movements simulation) and during the intervention (prostate biopsy and brachytherapy simulation). In cellular biology, the model is used to study phenomenons at the cellular level for simulating micro-manipulations experiments, where classical approaches could can only give a partial representation. This manuscript is developed in three parts : chapter 1 presents a general introduction on soft tissue modeing for Computer Assisted Medical Intervention and cellular biology ; chapters 2 to 5 present the model, its validation and its different applications ; and the last chapter, chapter 6, presents some prospect for this work. Appendix A is a synthesis of my activities (short CV). This work has leed to the supervision of Master and PhD students (see list in appendix B) ; and to scientific and clinical collaborations (see list in appendix C). My publication list is given in appendix D and the most significant/recent articles are given in appendix E.