The bunching of cathode rays in the klystron, described in this Journal by R. H. Varian and S. F. Varian, is treated mathematically here, and is found to result in a current having a wave form with sharp peaks and containing strong higher harmonics. In the absence of appreciable ``de‐bunching'' by mutual repulsion, the kinematics of the bunching process leads to specifications for an optimum condition of bunching and to the prediction of an ideal efficiency of 58 percent for the conversion of the cathode‐ray power into high frequency power. De‐bunching becomes important under certain calculated conditions, limiting the amplification factors obtainable in amplifiers without regeneration. It also changes the optimum conditions for oscillators and reduces their efficiencies by calculable amounts. The power required in the buncher is relatively very small and depends on the buncher voltage almost like that of an additional ohmic resistance.