A new modulation technique, π/4-Controlled Transition PSK (π/4-CTPSK), suitable for non-linearly amplified digital mobile satellite communications systems is introduced. This technique is derived from π/4-QPSK, the modulation scheme adopted as the new U.S. and Japanese digital cellular standard. The π/4-CTPSK modulated carrier is shown to undergo significantly less spectral regeneration after non-linear amplification compared to π/4-QPSK, leading to more efficiant utilization of the available power and spectrum. A principal application of π/4-CTPSK is for systems which may require differential or discriminator detection, such an low bit-rate satellite and land mobile radio communications.