The `Spinning Enhanced Visible and InfraRed Imager' will be flown on the Meteosat Second Generation satellites. The mission objectives and major performance requirements of the instrument are presented. The features of the 12 channels covering a wide spectral range from 0,5 micrometers in the visible region to 14 micrometers in the infrared domain are described, with their dedicated applications: Basic Multispectral Imagery, Cloud Motion Vectors, High Resolution Imagery, Air Mass Analysis and Surface Parameters. The instrument design and operating principle are described. Telescope and Scan Assembly, Focal Plane and Cooler Assembly, and Instrument Control & Data Handling regroup the most challenging optical instrumentation technologies. Expected instrument radiometric performances are summarized; improved spatial, temporal, spectral and radiometric resolutions will allow the image data to be used in future Numerical Weather Prediction processes. The overall program development plan foresees the manufacturing and testing of 3 satellites, the first launch being planned for the dawn of the next millennium.