Lightning observations from satellites in low Earth orbit have been made over the past 25 years, producing estimates of global flash frequency by season and latitude as well as information on diurnal variations. However, these measurements have suffered from low detection efficiencies, poor spatial resolutions, and the inability to continuously monitor specific storms or storm systems. Using results of investigations with a high-altitude NASA U-2 aircraft and other research, a space sensor capable of mapping both intracloud and cloud-to-ground lightning discharges from geostationary orbit during day and night with a spatial resolution of 10 km and a detection efficiency of 90% is currently being developed. In addition, this sensor, which is called the Lightning Mapper Sensor (LMS), will monitor storms on a continual basis. The combination of modern solid state mosaic focal planes with extensive on-board signal processing in the LMS provides a powerful technique for the detection of weak background-contaminated signals and permits the detection of lightning during the day. The LMS has a 10.5° field of view that covers all of the continental United States, large oceanic areas, all of Central America, much of South America including the Andes and the Amazon Basin, and large regions of the intertropical convergence zone. It is anticipated that the LMS will be flown on a GOES satellite in the mid-1990s. The characteristics and design of the LMS are presented as well as a discussion of the scientific research that will be possible with this instrument.