In his book The Limits of Liberty, Professor Buchanan argued that the state has two roles, that is, “protective” and “productive” ones, which are derived from the viewpoint of gains-from-trade among individuals. The purpose of this paper is to elucidate the characteristics of his view of the state described in this book and his essays.Professor Buchanan's theory of the state is characterized by (methodological) individualism, contractarianism, constitutionalism, libertarianism, subjectivism and democracy. All these elements are important and closedly linked each other. It should be emphasized, however, that contractarianism and constitutionalism, along with individualism, are specially important elements. And it should be pointed out that his libertarianism substantially means the constitutionalist-contractarian position based on individualism. Indeed, his own peculiar libertarianism distinguishes him from the libertarian anarchists, Hayek, Rawls and others. In this paper, we consider the difference between these modern thinkers and Buchanan in more detail.