This lesson presents the scientific and technical basis for using visible and infrared satellite imagery so forecasters can make optimal use of it for observing and forecasting the behaviour of the atmosphere. The concepts and capabilities presented are common to most international geostationary (GEO) and low-Earth orbiting (LEO) meteorological satellites since their inception, and continue to apply to both current and newer satellite constellations. The lesson reviews remote sensing and radiative transfer theory through a series of conceptual models. Discussions contain explanations of the different Meteosat First Generation imager channels and the phenomena that they can monitor individually and in combination. This lesson is an online version of the first ASMET (African Satellite Meteorology Education and Training) lesson published on CD-ROM in 1997. Conversion to HTML is courtesy of EUMETSAT. While the images have not been updated, the concepts are fundamental and remain relevant today. Most of the images are from Meteosat and depict weather conditions over Africa, although some GOES imagery is included as well.