Plants expressing genes encoding -endotoxins (cry genes) from the bacterium Bacillus thuringiensis (Bt) have triggered great interest for the control of agronomically important insect pests. A wide variety of plant species has been transformed with genes coding for various toxins aimed mainly at Lepidopteran and Coleopteran pests. The first transformation experiments conducted with bacterial genes (wild-type or native genes) have shown that the level of expression of these genes in plants is usually too low to confer good protection. To circumvent these problems, Bt toxin genes have been partially modified or totally re-synthesized, dramatically improving their level of expression in plants. Despite these improvements, some problems remain. In particular, the control of less susceptible insects, and that of the safe deployment of transgenic plants in relation to the emergence of toxin-resistant insects has yet to be addressed.