The lidar (laser radar) technique of remotely observing atmospheric structure and composition is now ready for use on a space vehicle. Progress in lidar technology has led to the development of high performance, light-weight, compact and highly reliable basic systems. These could ensure successful mapping of clouds and aerosols by elastic backscattering and offer high promise of opening up a range of more sophisticated observations using wavelength-specific techniques (resonant scattering, differential absorption and Doppler). The Spacelab program provides an ideal facility for initiating and exploring this concept, since it makes possible development on a short-trip, minimum-investment basis. The goals, philosophy and rationale of a proposed program to accomplish the first use of lidar in space are described, and details are provided of the specific observations proposed and of the necessary instrumentation. Using a solid-state neodymium laser, frequency doubled to drive a tunable, doubled dye laser, energy could be transmitted at a range of wavelengths (1060 nm, 589 nm, 530 nm and 279.6 nm). With simple wavelength-discriminating photometric detectors the system could be used to detect returns from particles (cloud and dust) or Na atoms or Mg+ ions. The value of a capability to make such observations is noted in terms of their meteorological and aeronomical significance.