The Advanced Technology Microwave Sounder (ATMS) is under development by NASA GSFC. The first ATMS Flight Unit will fly on the NASA, NPOESS Preparatory Project (NPP) satellite, and ATMS production units will be part of the National Polar-orbiting Operational Environmental Satellite System (NPOESS) sensor suite. This paper presents key instrument design features, channel characteristics, predicted performance, recent development status and the NPOESS plan for ATMS.