Genetically modified organisms (GMO) raise societal, political and ethical concerns. They inspire strong resistance or, conversely, enthusiastic assent. The aim of this publication is to give an overview of genetic engineering, starting with the history of the discovery of restriction enzymes continuing with technical aspects of transgenesis to its applications in research and ethical considerations. Be it the use of single engineered cells or GMO, these applications cover a broad array, ranging from disease-oriented research (but not only), to the promising perspectives of gene therapy. Historical and technical aspects give insights into the problems inherent to the creation of GMO, and illustrate the links and limits between genetic engineering, GMOs and gene therapy. A summary article in English and French structures the links between the different chapters and concepts. Scientists interested in genetic engineering of single cells or animal models, as well as in gene therapy, will find an up-to-date review on the use and perspectives of transgenesis. However, this publication is also recommended to the public interested in the definition of GMO, which encompasses a much broader array than the genetically modified crops covered by media.