The advent of biotechnology has created new potential opportunities in the improvement of the major agricultural crops for the benefit of the farmer and the food processor. The regulations, in different countries of the world, governing the release and commercialization of genetically engineered plants has inhibited the full exploitation of the technology. Other areas of biotechnology, not constrained by regulations, such as molecular markers, are however, already being used by plant breeders. Research and application of genetic engineering to commercial tobacco improvement has not been as rapid as might have been expected considering that tobacco, albeit with non-commercial varieties, has been used as a model species for this type of work. Genetic engineering involves either the addition of novel genes or the suppression of existing genes in transgenic plants. Novel genes may come from different sources, for example the same species, other plant species or bacteria. The expression of the novel genes can be regulated by the use of different promoters so that the gene is only expressed in certain tissue or at a particular stage of plant development. Suppression of gene expression can be brought about by antisense technology . The addition of a gene(s) or suppression of gene expression can be classified by the type of change which results in the plant : a new novel trait such as herbicide, insect or nematode resistance; modifications to existing metabolic pathways (metabolic engineering) such as qualitative and quantitative changes in carbohydrates, lipids or secondary products; and modification to plant development and physiology such as apical dominance and tolerance to stress conditions. Most progress has been made on the first group with numerous field trials throughout the world examining transgenic plants that are resistant to herbicide and insects and exhibit male sterility. The second group has attracted the attention of food processing or downstream agricultural businesses where modifications to pathways are being made to reduce processing costs or increase product quality. Genetic engineering for changing plant development in most cases is more complex and less well understood but offers potential for the future.