  Detailed observations of a growing number of supernovae have determined a
bloom of new peculiar events. In this paper we take a short tour through the SN
diversity and discuss some important, physical issues related to it. Because of
the role of SN Ia in determining the cosmological parameters, it is crucial to
understand the physical origin of even subtle, observed differences. An
important issue is also the reddening correction. We belive that the measure of
interstellar lines on medium resolution spectra of SNe can be used to derive
lower limits on the interstellar extinction. A few physical parameters of the
progenitor, namely radius, mass, density structure and angular momentum, may
explain most of the diversity of core-collapse events. In addition, if the
ejecta expand into a dense circumstellar medium the ejecta-CSM interaction may
dominate the observed outcome and provide a mean to probe the mass loss history
of the SN progenitor in the last stages of its evolution.
