The usefulness of energy dissipation devices to reduce seismic response of structures is now well established. For a given installation of such devices in a structure, one can easily compute the level of response reduction achieved. However, the solution of an inverse problem of how many devices one would need to achieve a desired level of response reduction in a structure, or to achieve an expected level of performance from a structural system, is not quite as straightforward and well formulated. In this paper, a method is presented to obtain the amount of viscous and visco-elastic damping one would need to obtain a desired level of response reduction. The needed supplemental devices are also optimally distributed in the structure to achieve the best performance. To solve the optimal problem, a gradient-based optimization approach is used. To illustrate the application, numerical results for a 24-storey building structure are presented where the objective is to achieve the maximum reduction in the performance functions expressed in terms of the inter-storey drifts, base shear, or oor accelerations. Other forms of performance functions can also be treated similarly.