Several optimum and suboptimum isolators are discussed with respect to three different criteria appropriate to shock and vibration isolation. In attempting to show the limitations of performance of a system optimized according to one criterion when considered from the point of view of another criterion, a number of advantages and disadvantages of the optimum systems are made evident. The results are presented in trade-off diagrams which allow a continuous range of choice in penalizing measures of relative displacement and the force or acceleration associated with the isolated element.