One of the instruments to be launched on ENVISAT around the turn of the century is the Scanning Imaging Absorption spectroMeter for Atmospheric Cartography (SCIAMACHY). This eight-channel spectrometer covers the wavelength range of 240 nm to 2385 nm and will allow the first space-borne simultaneous atmospheric measurements in the ultraviolet, visible and near-infrared. Furthermore, since the instrument is capable of measuring spectra of the sun light scattered/transmitted by the Earth and its atmosphere is nadir, limb and sun-occulation mode, it will allow obtaining 3D images of atmospheric trace gases and aerosol, with global coverage in three days. These data will greatly enhance insight in the dynamics and the long-term behavior of the constituents of the Earth atmosphere. The instrument is designed and built as a joint Dutch/German project, funded and supervised by the respective National Space Agencies. The Dutch partners, TNO-TPD, Fokker Space and SRON, are responsible for the Optical and Radiant Cooler Assemblies, the German main contractor Dornier for the Electronic Assembly. At present SCIAMACHY is well in its C/D phase: the structural models have already demonstrated their capability to withstand the launch vibrations and loads, the electronic, the optical and the radiant cooler assembly are all nearing their completion, calibration facilities have been built or updated, and the verification of their requirements has been planned in detail. This contribution will give an overview of the current status of the instrument and point out some of the challenges one had to face. In particular we will focus on the optical assembly, the heart of SCIAMACHY.