Abstract : The performance of off-axis optical communication receivers is considered. A statistical model of the photodetection process is presented and the influence of the received field statistics on the photodetection process is discussed. Upper and lower bounds on the probability of bit error for binary, one-shot, digital communication systems utilizing direct detection are developed. These bounds are based on the Bhattacharyya distance measure. A computer program is developed, which when interfaced with existing programs that model the propagation of optical radiation through the atmosphere, predicts the probability of bit error performance for off-axis optical communication systems. (Author)