Part I provides an introduction to this study of players' beliefs and decision rules in to obtain data in order to public good games. The experimental method will be used test theoretical ideas about beliefs and decision rules. Chapter 1 discusses some methodological issues concerning experimentation in the social sciences. In particular, this chapter focuses on the relationship between experimental economics and social psychology. Chapter 2 provides an overview of psychological and economic ideas concerning players' beliefs and decision rules in public good games. This chapter forms the theoretical foundation of the book. Chapter 3 discusses some basic experimental tools which will be used in the experiments to be reported in part II. These basic experimental tools make up two procedures, to obtain a measure of a player's social orientation and a measure of her or his beliefs. 1. Experimentation in the social sciences 1.1 Introduction The study of human behavior is an area where economics and psychology overlap. Although both disciplines are concerned with the same human beings, they often have different points of view on how people make choices and the motivation behind it.