The phenomenology of 3-neutrino mixing,
the current status of our knowledge about the
3-neutrino mixing parameters, including
the absolute neutrino mass scale,
and of the Dirac and Majorana CP violation
in the lepton sector, are summarised.
The seesaw mechanism of neutrino
mass generation and the related leptogenesis
scenario of generation of the baryon asymmetry
of the Universe are briefly discussed.
The results showing that the CP violation
necessary for the generation
of the baryon asymmetry of the Universe
in leptogenesis can be due exclusively to the Dirac
and/or Majorana CP-violating phase(s) in the
neutrino mixing matrix $U$ are reviewed.