Remote sensing applications continue to place increasingly strict specifications on laser systems. High pulse.energy and short-duration pulses relate directly to range and spatial resolution capabilities Of laser-based atmospheric sensors. Frequency agility of the laser adds the dimension of differential absorption and differential scattering measurements for quantitative studies of atmospheric molecules and aerosols. High spectral purity of the laser transmitter pulse permits the use of heterodyne detection for improved signal-to-noise measurements and makes the studies of small Doppler-induced frequency shifts caused by relative motion between target and observer possible. Laser Science, Inc. has built a high-spectral purity, injection locked CO2 laser transmitter for remote sensing and target ranging applications. The purpose of this paper is to discuss the design details and the theory of operation of this laser transmitter.