The mass distribution in Spirals
  In the past years a wealth of observations has unraveled the structural
properties of the Dark and Luminous mass distribution in spirals. These have
pointed out to an intriguing scenario not easily explained by present theories
of galaxy formation. The investigation of individual and coadded objects has
shown that the spiral rotation curves follow, from their centers out to their
virial radii, a Universal profile (URC) that arises from the tuned combination
of a stellar disk and of a dark halo. The importance of the latter component
decreases with galaxy mass. Individual objects, on the other hand, have clearly
revealed that the dark halos encompassing the luminous discs have a constant
density core. This resulting observational scenario poses important challenges
to presently favored theoretical $\Lambda$CDM Cosmology.
