Thus far in this book we have dealt with the optimization of single-degree-of-freedom systems with isolators. Such systems are governed by second-order ordinary differential equations. In the present chapter, we consider some problems of optimal isolation for systems which are described either by a higher-order set of ordinary differential equations or by partial differential equations. The mathematical models presented in this chapter can be applied to a number of systems, including biomechanical systems and structures under seismic or wind loads.