Genetic engineering of crop plants has been in progress since the dawn of agriculture, about 10 000 years ago. For millennia the genetic make-up of our crop plants has been changed by mankind's selection of naturally occurring variants. As the trade routes were developed, novel plant types were introduced into new environments and provided more variation from which to choose. At the end of the nineteenth century an understanding of the laws of heredity was gained and plant breeding protocols were devised whereby selection became accompanied by deliberate crossing. As the knowledge of the genetic structure of crop plants improved, new ways of manipulation were invented and exploited. Indeed plant breeding became a testing bed for new ideas in genetics. For the plant breeder the techniques which were most widely employed in the past were those which aided breeding, for example techniques which speeded up the production of new varieties, but still used traditional routes of crossing and selection. This was a transitional phase between plant breeding as an art and plant breeding as a science.