Vibration isolation systems are used in a large variety of applications (automotive, buil- dings, spatial structures such as aircrafts, satellites and in rotating machines) in order to reduce the transmission of mechanical vibrations from the equipments toward the foun- ation or viceversa. An isolation is obtained inserting a mechanical component (isolator) that acts as a link between the source subsystem and the isolated subsystem. There are two quantities generally used to evaluate the e®ectiveness of a isolation system: the trans-missibility and the power transmitted. In this work, it has been used the power, being this the most generic methodology that can be easily used in complex systems, but it has the disadvantage of a di±cult experimental validation. In this thesis, it will be studied numerically several passive isolation systems with rigid or °exible components, these will be modeled by theirs mobility or impedance matrices. This matrices are achieved by analytical or numerical methods depending of the convenience in each case. Generally traditional projects of isolation systems consider a unidirectional excitation and evaluate only some components of the response system, this occurs for the limitations in the trans-missibility use. Moreover, they do not give an appropriate attention to some parameters of geometrical con¯guration of the system (location and angle inclination of the isolators, location of the base supports, etc.). Herein, it will be shown the relevance of this pa-rameters in the search process of optimal con¯gurations and it will be also see how they depend strongly on the kind of the system excitation, so it will be used some combinations of multidirectional harmonic excitations.