Three important factors in a vibration isolation problem are the characteristics of the vibrational source, the structure at the point of attachment, and the coupling element or isolator. The structure is considered a single port element and is represented by its driving point impedance. The source is considered an active single port element, and it is represented by a Thevenin or Norton equivalent circuit determined from measurements. Isolators are considered passive two ports and are represented by π orTequivalent circuits as determined from measured impedance or mobility parameters. The first step in isolating a small electric motor from a nonrigid structure was to determine the impedance representations by direct measurements at the points of connection. Then the motion of the structure was predicted and measured as a reference for isolator effectiveness. After considering the characteristics of the source and the structure, a simple isolator was designed. The effectiveness was predicted and then measured. The equivalent circuits of several other isolators, including commercial types, were determined and their effectiveness measured.