  The properties of supernovae (SNe) are reviewed. It is shown that the
observed characteristics of the morphological classes of SNe (types Ia, Ib/c,
II) can be explained in terms of two basic explosion mechanisms, i.e. core
collapse of massive stars and thermonuclear explosion of low/moderate mass
stars.
  The study of SNe can provide valuable insight in the late phases of the
evolution of their progenitors and, therefore, can constrain the theory of
stellar evolution quite tightly.
  Also, bright SNe of type Ia can be used to probe the Universe up to high
redshifts, allowing us to measure cosmological constants and to gain valuable
information on the formation and evolution of galaxies.
  The case of SN 1987A is discussed in some detail: it appears that in this
event a number of predictions were astonishingly well verified but still many
aspects were completely at variance with "common wisdom" expectations,
indicating that the SN phenomenon is still not fully understood.
