Lidar systems are now widely used for diagnostics of the atmosphere. These systems employ the backscattering of laser radiation to provide information on atmospheric parameters via a number of scattering and absorption processes. The field has progressed rapidly in recent years and many high-performance lidar systems are now in operation around the world. These systems use lasers in the ultraviolet, visible, and infrared, and are able to make quantitative measurements of many atmopsheric parameters. In this paper the lidar field is reviewed. Present lidar systems are described and the current measurement capabilities are summarized.