Since the beginning of the VISIR project, the calibration aspects have been taken into account as an integral part of the design. In order to provide the user and the archive with high quality and well-controlled data, it is mandatory to have, during the routine observation phase, all calibration observations as part of the instrument set-up activities and as part of the actual Astronomical Observing Template. We propose here to review the calibration of VISIR observations. After a description of the various hardware
tools which have been introduced for calibration purposes (warm calibration unit, distortion grid, pupil imaging optics, wavelength calibration modules), we will present the calibrations in four astronomical categories (spatial resolution, photometry, astrometry and wavelength calibration). Cross-calibrations between the Imager and Spectrometer subsystems will also be addressed.