Public Choice is an interdisciplinary academic approach to analyzing public institutions using rational choice reasoning. Economics examines choices among consumer goods and investments; political science considers the dynamics of group choice, given rules. Public Choice differs from either in that rules themselves are the object of analysis and selection. Founded in reaction to the orthodox “market failure” justification for regulation, Public Choice considers “government failure” as an argument against the use of state-driven coercion over private choices. For the most part, Public Choice accepts the legitimacy of government, especially in the areas of defense, police power, and dispute resolution, but it explores constitutional restrictions on the expansion of discretionary power, by “limiting Leviathan.” The key concepts that Public Choice has contributed to libertarian thought include (1) Rent-seeking; (2) Government failure; (3) Majoritarian instability; (4) Collective action problems; and (5) Federalism and exit provisions as a limit on state power.