This work contains a description of the properties of G, K and M stars necessary to interpret their behaviour in the Geneva photometry. The properties of the Geneva system are discussed and a multidimensional classification is proposed for the G and K stars, dwarfs and giants. Calibrations in absolute magnitude, effective temperature and metal content are provided as well as methods for the detection of pecularities and multiplicity. Examples of application to the study of the galactic structure are given in the last chapter.