 Game trees and game matrices specify the moves available to players at different moments in time. They also indicate all possible outcomes, either as cells in a matrix, or as leaf nodes in an extensive game. However, to study what players should or will do in a game, a further component is needed: players’ preferences. Such preferences need not only reflect material pay-offs or other features of outcome states. Rather, they may also relate to the process of play itself, and which moves lead to a certain outcome. Moreover, preferences may contain irreducibly subjective elements. Even when assuming the same role in a game, different players may disagree about the relative desirability of certain outcomes (Fehr &amp; Schmidt 1999).