Abstract
The theoretical background for the main scaling relations of spiral galaxies is discussed, and compared with the observational datum. The luminosity-linewidth relation (TFR) is the best determined among those; the sources of scatter of each are discussed. The results of applications of the TFR to Cosmology, using several all-sky samples of galaxies, are summarized. They yield estimates of H[o], of the linearity of the Hubble flow, of the peculiar velocity field and its convergence depth and of the mass density parameter.
