Epistemic game theory views rational decision making in games as something not essentially different from rational decision making under uncertainty. As in Decision Theory (Peterson 2009), to choose rationally in a game is to select the “best” action in light of one’s beliefs or information. In a decision problem, the decision maker’s beliefs are about a passive state of nature, the state of which determines the consequences of her actions. In a game, the consequences of one’s decision depend on the choices of the other agents involved in the situation (and possibly the state of nature). Recognizing this—i.e., that one is interacting with other agents who try to choose the best course of action in the light of their own beliefs—brings higher-order information into the picture. The players’ beliefs are no longer about a passive or external environment. They concern the choices and the information of the other players. What one expects of one’s opponents depends on what one thinks the others expect from her, and what the others expect from a given player depends on what they think her expectations about them are.