  We show that grand unified theories based on SO(10) generate naturally the
next-to-leading baryon number violating operators of dimension seven. These
operators, which violate B-L, lead to unconventional decays of the nucleon such
as n -> e^-K^+, e^- \pi^+ and p -> \nu \pi^+. In two-step breaking schemes of
non-supersymmetric SO(10), nucleon lifetime for decays into these modes is
found to be within reach of experiments. We also identify supersymmetric
scenarios where these decays may be accessible, consistent with gauge coupling
unification. Further, we show that the (B-L)-asymmetry generated in the decays
of GUT scale scalar bosons and/or gauge bosons can explain consistently the
observed baryon asymmetry of the universe. The induced (B-L)-asymmetry is
sphaleron-proof, and survives down to the weak scale without being erased by
the electroweak interactions. This mechanism works efficiently in a large class
of non-SUSY and SUSY SO(10) models, with either a 126 or a 16 Higgs field
employed for rank reduction. In minimal models the induced baryon asymmetry is
tightly connected to the masses of quarks, leptons and neutrinos and is found
to be compatible with observations.
