  In the standard model and most of its extensions the electroweak transition
is too weak to affect the cosmological baryon asymmetry. Due to sphaleron
processes baryogenesis in the high-temperature, symmetric phase of the standard
model is closely related to neutrino properties. The experimental indications
for very small neutrino masses from the solar and the atmospheric neutrino
deficits favour a large scale of B-L breaking. For hierarchical neutrino
masses, with B-L broken at the unification scale $\Lambda_{GUT} \sim 10^{16}$
GeV, the observed baryon asymmetry $n_B/s \sim 10^{-10}$ is naturally explained
by the decay of heavy Majorana neutrinos. The corresponding baryogenesis
temperature is $T_B \sim 10^{10}$ GeV. In supersymmetric models implications
for the mass spectrum of superparticles can be derived. A consistent picture is
obtained with the gravitino as LSP, which may be the dominant component of cold
dark matter.
