This paper gives a summary of theoretical and practical studies on the properties of pulse-phase modulation, developed mainly in 1943.The properties of pulse-phase modulation are studied by means of Fourier transformations. Although some approximations are introduced, the calculations lead to the following definite conclusions:(1) Pulse-phase modulation introduces no amplitude distortion except at sub-multiples of the recurrent frequency.(2) The harmonic distortion, if any, is negligible and this method of modulation can be used for high-quality broadcasting.(3) Pulse-phase modulation is subject to a special type of distortion called “cross-distortion,” produced by side bands of the recurrent frequency appearing in the signal bandwidth. Curves of the approximate amount of this type of distortion are given, and it is shown that, in practical multi-channel systems, this distortion is negligible, provided that the recurrent pulse frequency is at least double the highest signal frequency to be transmitted, and preferably equal to, or greater than, three times this frequency.This study is followed by considerations on the signal/noise ratio in pulse-phase modulation. Pulse-phase modulation is compared with amplitude modulation and a formula, giving the improvement in the signal/noise ratio due to pulse-phase modulation, is established by very simple considerations. It is shown that this ratio improves as the frequency bandwidth used in pulse-phase modulation.It is shown how an improvement of 3 db in signal/noise ratio can be obtained by suppressing the noise on the synchronizing pulse, and a practical circuit developed and applied in 1943 by the author is described.Finally, a typical example of pulse technique is given. In practical circuits the modulator and demodulator pulses are not perfectly shaped, because of the departure from linearity due to finite time-constants. This introduces harmonic distortion. It is shown how this distortion can be practically eliminated by designing circuits so that the time constant is equal at modulation and demodulation.