A treatment of the acceleration of particles by the linear resonance accelerator is given, including the calculation of the velocity distribution of particles emergent from the device and a method for improving the yield and the velocity distribution. Calculated curves showing these features are shown. The mass selection properties of the device are also considered. Focusing is considered briefly and a discussion of the characteristics of a quarter wave‐length line as applied to a resonance accelerator is included. The experimental features of a linear accelerator as built up are described. Probable particle energies to be expected from any future device of the kind are indicated.