The manner in which the internal damping and the dynamic elastic moduli of rubberlike materials depend upon frequency and temperature is described in detail. Examples are presented of the frequency dependence of the dynamic shear modulus and shear damping factor of low- and high-damping rubbers in the range 1 c/s through 10 kc/s at the temperatures 5, 2o and 35° C. These results have been deduced by the method of reduced variables from the experimental data of other workers. They relate to the low-damping materials natural rubber, natural rubber reinforced with carbon black, and SBR rubber; and to the high-damping materials Thiokol RD rubber, butyl rubber reinforced with carbon black, and plasticized polyvinyl acetate. The principles of vibration isolation are reviewed briefly. A simple general equation is derived from which the transmissibility any rubberlike material may be estimated, provided the frequency dependence of the dynamic shear modulus and the associated damping factor of the material are known. From this equation, the desirable physical characteristics of an effective vibration isolator are readily made apparent. Representative computations made from the general transmissibility equation are described; these computations incorporate numerical data that have been presented graphically for several of the foregoing low- and high-damping rubbers. The possible influence upon the transmissibility curves of nonlinear rubberlike behavior is discussed briefly. Detailed consideration is given to so-called wave effects that may occur at high frequencies, when the dimensions of the vibration isolator become comparable with multiples of the half-wavelength of the elastic wave traveling through the component rubberlike material. Thus, computations of transmissibility have been made from an expression derived with the assumption that the rubberlike materials obey the wave equation for the longitudinal vibration of a “long” rod of uniform cross-section. The results of these computations, which relate to the same rubbers as considered previously, are compared with the results obtained from the simple transmissibility equation. In the case of high-damping rubbers, the simple and more complex theories are found to be in good agreement. In the case of rubbers with relatively small damping, the effectiveness of the isolators at high frequencies is overestimated by the simple theory although, at these frequencies, the transmissibility of the isolators will normally remain a small quantity.