  We make generic remarks about baryogenesis in models where the scale $M_s$ of
quantum gravity is much below the Planck scale. These correspond to M-theory
vacua with a large volume for the internal space. Baryogenesis is a challenge,
particularly for $M_s \lappeq 10^5$ GeV, because there is an upper bound on the
reheat temperature of the Universe, and because certain baryon number violating
operators must be suppressed. We discuss these constraints for different values
of $M_s$, and illustrate with a toy model the possibility of using horizontal
family symmetries to circumvent them.
