 Game theory may be understood as generalized interactive decision theory. A major vehicle for the latter, just as for standard decision theory, is probability theory. Within games, probability can assume many roles. It may, for instance, express players’ degrees of belief quantitatively, but it can also enrich the space of actions with mixed strategies, thereby laying the ground for general equilibrium results. Probability can even play a role in the very definition of certain important games, especially in evolutionary game theory (Osborne &amp; Rubinstein 1994). In this entry, probability is only mentioned in passing.  Section 5,  however, maps some combinations of logic and probability that are suggested by the study of games.