This book focuses on the geostationary weather satellites and polar weather satellites. Geostationary environmental satellites play a critical role in our nation's weather forecasting. These satellite, which are managed by the Department of Commerce's National Oceanic and Atmospheric Administration (NOAA), provide information on atmospheric, oceanic, climatic, and solar conditions that help meteorologists observe and predict regional and local weather events. They also provide a means of identifying the large-scale evolution of severe storms, such as forecasting a hurricane's path and intensity. The Editors of this book discuss the National Polar-orbiting Operational Environmental Satellite System (NPOESS) program, planned to be a state-of-the-art, environment-monitoring satellite system that would replace two existing polar-orbiting environmental satellite systems.