Aristotle states that although political regimes vary from place to place, only one is by nature the best regime possible anywhere. The article analyzes some of the problems deriving from this statement, in order to show that the diversity of political forms is not abolished in that best regime and that conventional justice does not end up being superfuous. Furthermore, the Aristotelian idea of the best regime is radically diferent from later utopianism. Finally, the article examines the relation between the naturally just, as it is set forth in the Nicomachean Ethics, and the issue of the best regime, as dealt with in the Politics.