In this paper, effects of atmospheric turbulence on the Phase Shift Keying (PSK) modulation schemes of an electromagnetic wave carrier operating at optical frequencies are investigated. Tatarski's model for the atmospheric turbulence has been employed in these investigations. It is noted that the amplitude/intensity fluctuations of the optical carrier caused by the turbulent propagation medium will have are effect on this modulation scheme. The turbulent atmosphere through which the optical beam is propagating can also produce directly phase fluctuations which enhances the Bit Error Rate (BER) of the optical communication link. © 1994 SPIE. All rights reserved.