This volume presents an interdisciplinary approach to study individuals' decisions pertaining to public good games. Theories and ideas are extracted from both the field of economics and the field of social psychology. The empirical strength of different propositions is assessed in a series of experiments. These experiments are specifically designed to answer some conceptual questions. Examples of these questions are: Do players appreciate the strategic nature of the game? Do they learn from their experience? Are they concerned about the payoffs of other players? Do systematic differences exist between the decision rules of various players? <br/> <em>Beliefs and Decision Rules in Public Good Games</em> is divided into three parts. Part one provides an introduction to this study of players' beliefs and decision rules in public good games. The experimental method will be used to obtain data in order to test theoretical ideas about beliefs and decision rules. Part two provides the experimental results. The psychological as well as economic ideas are subjected to experimental testing. The final part provides a summary and interpretation of some of the results discussed in the previous chapters. It sketches the potential contribution of this study to the development of a positive theory of games.