For long-distance high-bit-rate optical communications it is desirable to have sources which operate in a stable single longitudinal mode and deliver maximum optical power to the receiver. One possibility Is to use phase-locked injection laser arrays which have been demonstrated to operate in a single longitudinal mode1,2 to output powers as high as 80-mW cw2 and in a single narrow beam to 200 mW.2 Strong coherent coupling between the array elements could in principle provide stable single-mode operation under modulation. Since these devices appear promising for high-power and/or single-mode applications in optical communications. we have developed the first model to utilize a coupled-mode analysis to describe the operation of phase-locked injection laser arrays. Previous analyses of phase-locked arrays have utilized simple diffraction theory3 which could only generally describe the experimental observations.