Experimental games are small, but expanding branch of economics. The major part of economics deals with large-scale phenomena like stock market fluctuations, rates of exchange, and gross national products. The trend in economic life towards globalization leads to ever more abstract and virtual forms of interaction, as can be seen by the rapid growth of global e-commerce, trading in licenses and options, and the like. Yet at the same time, paradoxically, economists become increasingly fascinated by interactions at the most down-to-earth level - the sharing and helping that goes on within office pools, households, families, or children groups. How does economic exchange work in the absence of explicit contracts and regulatory institutions?