This chapter describes necessary conditions for baryogenesis. It is remarkable that the couplings come as close as they do and this in itself lends general support to the Grand unified theory (GUT) hypothesis. The convergence represents the best evidence we have both for the GUT hypothesis and for low-energy supersymmetry and it is, therefore, natural to wonder whether a GUT with this matter content produces baryogenesis at the level needed to produce the observed asymmetry. The discussion of baryogenesis using the baryon-number non-conserving interactions of a GUT was based upon the assumption that the superheavy GUT gauge bosons or Higgs particles whose decays produce the desired baryon asymmetry are, in the first place, in thermal equilibrium and then, as the universe expanded and the temperature dropped, came out of equilibrium when the condition was satisfied. It is at least debatable whether this assumption is well founded.