  In this thesis, we study the role of flavours in leptogenesis. In a first
time, we review the so-called one flavour picture, where only the lightest
right-handed neutrino is taken into account, and where lepton flavours are
neglected. After having showed why and how lepton flavours should be included
in the computation of the lepton asymmetry, we study their effect in the type I
seesaw model, as well as in the type I+II seesaw model, in a specific SO(10)
unification realisation. In this model, besides flavours effects, we show that
the inclusion of the second lightest right-handed neutrino, together with an
accurate description of charged fermions masses, are necessary to make
leptogenesis work.
