This chapter introduces estimates and measurements of the pressure distribution in tissue. Several physical and computer models are included to show the results of estimating tissue pressure distribution. Experimental results suggest causes of pressure sore formation. Many researchers have worked to understand the pressure distribution inside the tissues. However, the human body is such a complicated medium that it is difficult to find a tissue substitute that can model it satisfactorily. Computers simplify complicated analyses. The finite element method (FEM) has been applied to many types of structures. A FEM model replaces the actual structure in a mathematical representation. This replacement makes software analysis possible for a complicated structure. Basically, a material is partitioned into finite elements. Each element is assumed to have isotropic parameters. A linear or piece-wise linear relation is applied within elements and between elements.