The issues of CO2 emission and climate change have become the most important problems in the world. There are two kinds, price control and quantity control, of economic instruments for the reduction of CO2 emission. The policy of price control is imposing the carbon tax. And the policies of quantity control include emission trading, joint implementation, and clean development mechanism that were proposed in 1997 Kyoto Protocol. This study will interpret these four different policies in terms of theoretical backgrounds, operation rules, benefits and costs, and their relationships. However, there is no theoretical model and no empirical model in the study. And this study only deals with the literature reviews.