Optically coupled lasers are a striking example of a class of self-organized nonlinear dynamic systems which are currently attracting much interest. From a practical standpoint, the coupling of lasers makes it possible to increase relatively simply both the output power and brightness of a light source. The present review gives an account of the current status of the theory and experimental results obtained for two or more optically coupled lasers. The stress is on the structure of collective modes and their stability. Frequency and phase locking of laser arrays is considered. Optical coupling systems tested experimentally are discussed and the agreement between the experiment and theory is considered. A description is given of the operation of systems in which lasers are detuned by an amount exceeding the width of a locking band. Methods for increasing the brightness of the output radiation of systems with a synthesized aperture are also discussed.