Since 2002-03-01 the spectrometer SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) is in a sun-synchronous polar orbit around the Earth aboard the new European environmental satellite ENVISAT. SCIAMACHY measures during its lifetime concentrations and distributions of atmospheric trace gases such as O3, BrO, OClO, ClO, SO2, H2CO, NO2, CO, CO2, CH4, H2O, N2O, metals, clouds, and aerosols. The quality of these data products depends both on the calibration of the instrument and the detailed knowledge of the instrument's status and behaviour at any time during the whole mission. To achieve this a comprehensive monitoring concept has been developed and implemented. This paper gives a brief overview of the instrument and the calibration and monitoring concepts. Results of the performance monitoring activities from nominal operations of the instrument show that SCIAMACHY in general is in good shape. The radiometric calibration of the instrument could be enhanced by a thorough revision of the on-ground calibration. An ice-layer buildup is observed on the IR detectors, which shall be compensated by a throughput correction factor.