The universe contains more baryons than anti-baryons. There are three key ingredients, attributed to Sakharov, for any theory that attempts to explain the size of the baryon excess: baryon number violation, C and CP violation, and a period of disequilibrium in the early universe. All of these ingredients are present in standard electroweak theory. Scenarios for electroweak baryogenesis depend on the rate of electroweak baryon number violation in the very hot, symmetry-restored phase of the theory -- a process which is non-perturbative. I will discuss the theoretical issues involved in understanding and calculating this rate.