The objectives of the seismic design of buildings can be achieved by applying techniques of conventional design that consider the that the ground motion is transmitted to the structure through its fixed base. As an alternative to this traditional design, base isolation systems were developed consisting of mechanisms that partially uncouple the structure of the foundation ground to reduce, in this way, the damages of the structure and of its content. Decoupling is carried out by placing support devices between the base of the structure and its foundation that increase the flexibility of the overall structure-base system and that produce, at the same time, an appropriate damping. Despite the large number of studies on different base isolation systems, there are few comparative analyzes between these systems. In this monograph, structures isolated with different systems are compared with structures with conventional design. To this end, criteria for evaluating the behavior of the different systems have been defined. In the numerical studies, models with linear behavior for the structure and nonlinear behavior of the base isolation system have been considered. The type of nonlinearity of the isolation is formulated by means of differential equations, capable of describing both hysteretic and frictional systems.