This book is addressed primarily to students of biology (bachelor's and master's degrees in biochemistry, cellular biology, physiology, and biology of organisms) as well as to students of the natural sciences who are preparing for competitive entrance examinations. With its numerous references to agronomic applications, it is useful to students in preparatory classes for the major agronomic schools as well as to students of shorter and specialized university courses ("Anabiotech" vocational training in biochemistry and plant production, technical institutes of applied biology). Two-year diploma students who wish to pursue their studies further can also benefit from this book. The first part of the book is devoted to a recapping and integration of the essentials of plant biology, agronomy, and molecular biology so as to be able to address more easily the techniques, concepts, and stakes of plant biotechnology in the various sectors in which it exerts its influence, including agro-food, health, environment, and energy. The second part contains a discussion of the principles and practice of techniques of everything concerning in vitro procedures, identification, and direct and indirect transfer of genes and the control of the functioning of trasgenes. Agronomic, bioindustrial, or environmental applications that are already practised are discussed in the third part of the book. Some considerations that are deliberately prospective are raised to identify sectors in which need, or sometimes simple curiosity, will drive active expansion of these technologies in the short and medium term. Bioethics, a moral, philosophical, and political discipline, imposed by advances in genetic engineering and the extraordinary development of these possible applications, is treated in the fourth part.