The place of genetics in biology makes its teaching unavoidable from secondary school onwards. However, this teaching is confronted with numerous pedagogical difficulties, not the least of which is the simple definition of a gene! Like any science, genetics is a set of mental representations of objects and phenomena of Nature. The objects that concern genetics in this book, as a science, are, at the center, the gene, its structure, its function, its mechanisms of expression, regulation, concerted action and development in plants, Population genetics, Quantitative genetics and, at the end, Genetic resources in plant breeding and improvement.