CCDs are widely used in astronomy, and are the major detectors for almost all of the instruments of the Isaac Newton Group. Descriptions of CCDs and their operation at a non-technical level are given in a number of astronomical publications; two recent reviews have been given by C.D. Mackay in Annual Reviews of Astronomy and Astrophysics, volume 24, page 255; and by P.R. Jorden in Modern Technology and its Influence on Astronomy, edited by J.V. Wall and A. Boksenberg, published by Cambridge University Press, page 271, 1990. A good introduction to the use of CCDs is also given by P.R. Jorden in ING La Palma Technical Note No. 93 (January 1994). The IRAF (Image Reduction and Analysis Facility) package is widely used for the processing and analysis of CCD data; documentation is available by anonymous ftp (iraf.noao.edu; see the iraf/docs directory and ccdguide.ps.Z in particular) and may also be found in binders in the WHT control room. The entire Starlink software collection, including the FIGARO package, is also available on all machines.