The reasons that impel researchers to use genetic engineering techniques to create GMOs are extraordinarily varied. Their activities have accordingly ranged from preoccupation with the most noble aims of purely scientific knowledge to commercial research for large multinational corporations. One particularly revealing development over the past 25 years has been common to all these aims: the reorientation of research projects of many biology laboratories. Genetic engineering very quickly was found to be a powerful and effective tool that could provide answers in some fields of research, of widely varying orientations, that have been stagnant or languished in dead ends. Research structures have been set up — laboratories, institutes, and centres—combining teams that not only have common research objectives, but also use the same molecular biology techniques, thus improving their access to costly materials such as oligonucleotide synthesizers or automated DNA sequencers. It is therefore not easy to classify simply and objectively the true reasons that have motivated operations of transgenesis in all the taxonomic groups representing the living world. Still, let us try to highlight, essentially for plants and their precious and indispensable auxiliaries, the microorganisms, the major objectives that are more or less acknowledged to be at the source of GMOs, objectives that have given rise to many of our concerns.