The differences between a dye and a pigment and the advantages and disadvantages of each are described. The three main hi-tech processes for producing colour hard copy, namely thermal, ink-jet and electrophotographic, are explained and the different requirements of colourants for each technology emphasised. In addition to providing the final print image, coloured molecules are also employed as key components in producing this image in electrophotography because of their electrical and photoelectrical properties. These are also discussed. © 1990.