  Superconductivity in Pb, H under extreme pressure and CaBeSi, in the
framework of the density functional theory for superconductors, is discussed. A
detailed analysis on how the electron-phonon and electron-electron interactions
combine together to determine the superconducting gap and critical temperature
of these systems is presented. Pb, H under pressure and CaBeSi are multigap
superconductors. We will address the question under which conditions does a
system exhibits this phenomenon. The presented results contribute to the
understanding of multiband and anisotropic superconductivity, which has
received a lot of attention since the discovery of MgB$_2$, and show how it is
possible to describe the superconducting properties of real materials on a
fully {\it ab-initio} basis.
