Cotton fibres, or lint, are very long single cells containing almost pure cellulose. The fibres develop in the weeks after flowering from single cells on the surface of the young seed. Each fibre cell is small at first but elongates and develops rapidly, eventually forming the mature cotton fibre. These processes require the ordered expression of genes which make enzymes, structural proteins and signalling molecules that together determine the properties of the fibre. Domestication has modified fibre development to produce cotton varieties with greatly improved fibre length, strength and quality. However, the selection and breeding of plants with desirable fibre characteristics is slow and expensive. As such, future crop improvement is likely to depend upon genetic engineering and the cotton industry has been a leader in both research and commercialisation of transgene technology, with momentous consequences for the agronomic properties of the crop such as insect and herbicide resistance. However, the potential for fibre modification by biotechnology has yet to be realised Apart from their commercial significance, the single-celled nature of cotton fibres and their synchronous growth inside the cotton boll has made them an attractive system for the study of plant cell elongation and cell wall biogenesis. Such fundamental studies have resulted in the identification of a number of genes with proposed roles in cotton fibre growth, and have led to the creation of the first molecular and cellular model of fibre development (Wilkins and Jernstedt, 1999). The model has provided the basis for limited early success in the alteration of fibre growth, but not on a commercial scale,