The first chapter details the different techniques of molecular markers, emphasizing genetic aspects, because these determine the type of use one can put it to. The construction of genetic linkage maps is the subject of the second chapter, where the advantages and disadvantages of the most common mapping populations are specified. The particular case of mapping of major genes, especially for the purpose of positional cloning, is addressed in the third chapter. Detection and applications of QTLs controlling the expression of quantitative traits are presented in the fourth chapter, which also tackles the complex question of their identification. The fifth chapter underscores the major contribution of molecular markers in the analysis of the structure and evolution of natural populations. Finally, the advantages of markers in selection, for studies of diversity and in the context of marker-assisted selection, are discussed in the last chapter. The authors have attempted to highlight the principles of markers, an