The Centre des Environnements Terrestre et Planetaires (CETP, previously called CRPE) is a research laboratory working in the field of environmental studies. CETP has a 15 year experience in microwave radiometry. The design, realisation and on-ground calibration of the ERS-1 microwave radiometer (ATSR/M) has been its major technical contribution in this domain. In parallel, CETP has developed methods for calibrating and validating space-borne microwave radiometers (SMMR,SSM/I,ATSR/M) in-flight, and for retrieving atmospheric and sea surface geophysical parameters. CETP is involved in the scientific use of microwave radiometer data in meteorology, particularly through the development of data assimilation in meteorological models, in collaboration with Meteo France and ECMWF. The group involved in CLIWA-NET owns two microwave radiometers, one built by RESCOM and the self-built transportable DRAKKAR.