  We review the scenario of baryogenesis through leptogenesis induced by the
out-of-equilibrium decays of heavy neutrinos. We pay special attention to the
resonant phenomenon of CP violation through mixing of two nearly degenerate
heavy Majorana neutrinos and show how unitarity and CPT invariance is
maintained within the resummation approach. An important consequence of this is
that the leptogenesis scale may be as low as 1 TeV, even for models with
universal Yukawa couplings. We briefly discuss the impact of finite temperature
effects and low-energy constraints to the afore-mentioned mechanism of CP
violation.
