If a rubber member is continuously vibrated it will sooner or later crack and ultimately rupture, owing to the repeated oscillations to which it has been subjected. The gradual deterioration of physical and chemical properties which accompanies such vibration is called dynamic fatigue. The number of such repeated vibrations required to rupture the rubber member is here defined as the dynamic fatigue life of the member for the particular condition of vibration imposed. The authors wish to outline briefly the general nature of the results they have obtained in their studies on the dynamic fatigue life of rubber and, in particular, to show the critical dependence of the life on the imposed oscillation conditions. The dynamic fatigue life of rubber which is being vibrated linearly, that is, back and forth along its own length, between constant strain limits will be discussed first. Figures 1 to 3 facilitate a general statement of the problem and also serve to define certain oscillation limits which are of fundamental importance with reference to dynamic fatigue life. The sketches are conventionalized for the sake of simplicity.