 Our topic is complicated by the fact that there are various alternative formalizations of probability. Moreover, as we will see, some of the leading ‘interpretations of probability’ do not obey all of Kolmogorov’s axioms, yet they have not lost their title for that. And various other quantities that have nothing to do with probability do satisfy Kolmogorov’s axioms, and thus are ‘interpretations’ of it in the strict sense: normalized mass, length, area, volume, and other quantities that fall under the scope of measure theory, the abstract mathematical theory that generalizes such quantities. Nobody seriously considers these to be ‘interpretations of probability’, however, because they do not play the right role in our conceptual apparatus.