  In the past years a wealth of observations has allowed us to unravel the
structural properties of the Dark and Luminous mass distribution in spirals. As
result, it has been found that their rotation curves follow, out their virial
radius, an Universal function (URC) made by two terms: one due to the
gravitational potential of a Freeman stellar disk and the other due to that of
a dark halo. The importance of the latter is found to decrease with galaxy
mass. Individual objects reveal in detail that dark halos have a density core,
whose size correlates with its central value. These properties will guide
$\Lambda$CDM Cosmology to evolve to match the challenge that observations
presently pose.
