Satellite observations have relied on passive remote sensing systems and thereby suffer a fundamental limitation in their accuracy and vertical resolution (2 to 4 km for remote sensing of atmospheric temperature). Lidar systems offer the potential for improved vertical resolution, accuracy, and with global coverage. To better understand important processes in the Earth system, these higher-resolution observations have now become a basic requirement for the satellite observing system of the 1990s. The author discusses the requirements for lidar observations of the Earth's atmosphere, land, and ocean surfaces, and the characteristics of the systems which will provide these observations.>