We review what we know about the "sphaleron rate", which is the efficiency of baryon number violation at high temperatures T approx 10- GeV in the Standard Model. The leading behavior at weak coupling in the symmetric phase is known accurately; #UPSILON# = (10.7+-.7)(g~2T~2/m_D~2)log(m_D/g~2T)#alpha#_w~5T~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 thanb perturbative estimates.
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