The Global Space-based Inter-Calibration System (GSICS) is an international collaboration to build an operational system for the inter-calibration of a variety of meteorological satellite instruments. GSICS is a critical thread that links individual observation system for integration into the Global Earth Observation System of Systems (GEOSS). This paper reviews the four categories of satellite instrument inter-calibration, reports on recent progress and current status of GSICS, and presents preliminary results from a prototype system.