The demand for low cost, quiet operation, and increased operator comfort in automobiles and other applications is requiring that new techniques be developed for noise and vibration isolation. One approach to reduce noise and vibration harshness is to develop a small low cost vibration isolator that can be used to mount components that generate vibration. To develop this isolator, passive, semi-active, and active control methods and different types of smart materials were studied. Based on this study, the most promising approach seems to be a semi-active magnetorheological isolator. An isolator of this type was designed to mount a compressor on an automobile body and to isolate the body from high frequency vibration produced by the compressor. This application is more difficult than the problem of isolating a component from vibration of a base because here vibration is also produced by the component. The new results that this study provides are: (i) a simulation model of a semi-active control system with a magnetorheological isolator, a low pass filter, and base and rotating unbalance excitations, (ii) detailed simulation studies showing the practical trade-offs between passive and semi-active isolator performance, and the effect of phase lag due to low pass filtering, and (iii) an electronically controlled isolator design that can turn filtering on or off to provide durability and isolation performance that cannot be achieved using a passive isolator alone. The isolator design proposed here can have several applications. These include engine mounts, pumps, and fans in automobiles, and the isolation of aviation and naval components where the isolator must be durable enough to withstand low frequency vibration and shock loading through its base, and at the same time prevent transmission of high-frequency vibration from the component to the mounting structure.