  I review what we know about the ``sphaleron rate'', which is the efficiency
of baryon number violation at high temperatures of order 100 GeV in the
Standard Model. The leading behavior at weak coupling in the symmetric phase is
known accurately; Gamma = (10.7 +- .7) (g^2 T^2 / m_D^2)
log(m_D/g^2T)\alpha_w^5 T^4. At realistic values of the coupling our accuracy
is worse. We also now have the tools to determine the rate nonperturbatively in
the broken electroweak phase; the sphaleron rate there is slower than
perturbative estimates.
