This paper reviews the present state of concepts and technologies of coherent optical space communications. Emphasis is placed on the receiving segment. Heterodyne and homodyne reception allows to realize sensitivities close to the theoretical limits which amount to as little as 10 to 40 photons per bit. They ask for a narrow-linewidth laser not only at the transmitter terminal but also as local optical source within the receiver. Coherent receivers require tight frequency control or even phase synchronization of laser radiation. In the laboratories, systems based on semiconductor lasers and on diodepumped Nd:YAG lasers were operated under frequency shift keying as well as with phase shift keyed modulation. Design studies performed in Europe and in the USA exemplify that coherent optical space links are the proper choice for a second generation, high-data-rate intersatellite communication system.