CRYSTALS is a well known and widely used software package for the refinement of x-ray crystallographic data and the solution of crystal structures containing small to medium size molecules in the unit cell. Its development at the Chemical Crystallography Laboratory in Oxford has been in progress for several years, initiated by J.R. Carruthers and further developed by many others most notably RW. Betteridge, R.L Cooper, K. Front, and D.J. Watkin assisted by a number of postgraduate students.