Soil pathogenic bacteria named Agrobacterium tumefaciens infect plants and cause tumours, called ‘crown galls’, by triggering the overproduction of hormones that control plant cell division. To achieve this, these special bacteria are capable of transferring a piece of their own DNA into the chromosomes of a few plant cells, programming them to proliferate and to form a tumour. The discovery of these mechanisms in the 70’s paved the way to the first, and still favorite, way of delivering foreign DNA to plants. Indeed, Agrobacterium strains have been produced that can be used as DNA vehicles, producing no more tumour but still capable of integrating DNA into plant chromosomes. Biotechnologists introduce genes of interest in the Bacterium using conventional techniques for these microorganisms and rely on the transformed bacteria to pass the genes to plant chromosomes. And it works !