In private international law, the public policy doctrine or ordre public concerns the body of principles that underpin the operation of legal systems in each state. This addresses the social, moral and economic values that tie a society together: values that vary in different cultures and change over time. Law regulates behaviour either to reinforce existing social expectations or to encourage constructive change, and laws are most likely to be effective when they are consistent with the most generally accepted societal norms and reflect the collective morality of the society.