POLDER is a radiometer dedicated to the observation of the polarization and directionality of the Earth's reflectances. It images the Earth with a large field of view (115 degrees) in 8 spectral bands from visible to near infrared. The instrument, developed by CNES will be installed on the ADEOS Japanese satellite to be launched in August 1996. This paper deals with the preflight radiometric and geometrical calibrations of the instrument. It presents the radiometric and geometrical models of the instrument, in relation with its physics. The geometrical calibration consists in determining for each spectral band the mathematical model relating each viewing direction within the instrument field of view to a pixel location in the focal plane. The requirement is to determine the absolute location of the image point with 0.05 pixel accuracy. The radiometric model takes into acount the different characteristics of the instrument, including the polarization capability and the bidimensional detector array. The scientific objectives of POLDER lead to severe radiometric calibration requirements (for instance, +/- 1% on relative low spatial frequency calibration or +/- 0.1% on relative high spatial frequency calibration). The dedicated ground equipments are described (integrating spheres, polarizers, reference radiometer, optical directional reference generator...), as well as the procedures and the first results with their related accuracies.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.