externalities may be nonpecuniary, the sort that produce inefficiency in competitive markets, or pecuniary, creating inefficiency due to an absence of competitive conditions In this section, I begin with some broad observations about the econom erspective on public international law. Because systematic discussions of international law often imagine that states behave as if they have"preferences, " the first topic concerns the conceptualization of states as rational actors. The analysis proceeds to a general discussion of customary international law, to a discussion of the economics of treaties, and finally to consideration of the interface between domestic and national law. A States as Rational Actors Positive economic analysis of international legal regimes conventionally proceeds from an assumption that states behave as if they are rational maximizers over some set of preferences regarding the outcomes of their interaction. The specific assumptions that may be made in this regard are myriad. States may be assumed to behave as economic welfare maximizers. or to maximize a social welfare function that weighs the welfare of certain constituencies more heavily than others. The preferences of the state"may be assumed to be those of its political leaders, who may maximize votes, campaign contributions, or their personal welfare. Innumerable other variations can be imagined depending on the context Whatever precise assumption is made about the nature of preferences, it common to embody a further assumption that states act as if they "care"primarily or exclusively about their own welfare or interests and less or not at all about the welfare ol interests of other states or their political leaders. A divergence will then arise between the national maximand and the global maximand e pr maximizers is surely somewhat simplistic. States represent an aggregation of many different actors, whose preferences may well be at odds. The actor with the power to choose among alternatives may change over time, and the constraints imposed on actors with the power to make choices can change over time(in the United States, think of the President as the actor with the power to make choices on international matters, subject to constraints imposed by Congress). Even when it is plausible to assume that a pertinent decisionmaker has a preference ordering over the available alternatives at a point in time therefore, the notion that the"preferences"of the state are stable over time, or that they obey potentially important regularity assumptions, may be quite problematic Although one must acknowledge this problem, there is often little to be done about it in a tractable modeling framework beyond remaining attentive to its possibleexternalities may be nonpecuniary, the sort that produce inefficiency in competitive markets, or pecuniary, creating inefficiency due to an absence of competitive conditions. In this section, I begin with some broad observations about the economic perspective on public international law. Because systematic discussions of international law often imagine that states behave as if they have “preferences,” the first topic concerns the conceptualization of states as rational actors. The analysis proceeds to a general discussion of customary international law, to a discussion of the economics of treaties, and finally to consideration of the interface between domestic and national law. A. States as Rational Actors Positive economic analysis of international legal regimes conventionally proceeds from an assumption that states behave as if they are rational maximizers over some set of preferences regarding the outcomes of their interaction. The specific assumptions that may be made in this regard are myriad. States may be assumed to behave as economic welfare maximizers, or to maximize a social welfare function that weighs the welfare of certain constituencies more heavily than others. The preferences of the “state” may be assumed to be those of its political leaders, who may maximize votes, campaign contributions, or their personal welfare. Innumerable other variations can be imagined depending on the context. Whatever precise assumption is made about the nature of preferences, it is common to embody a further assumption that states act as if they “care” primarily or exclusively about their own welfare or interests, and less or not at all about the welfare or interests of other states or their political leaders. A divergence will then arise between the national maximand and the global maximand. The assumption that states have preference orderings and act as rational maximizers is surely somewhat simplistic. States represent an aggregation of many different actors, whose preferences may well be at odds. The actor with the power to choose among alternatives may change over time, and the constraints imposed on actors with the power to make choices can change over time (in the United States, think of the President as the actor with the power to make choices on international matters, subject to constraints imposed by Congress). Even when it is plausible to assume that a pertinent decisionmaker has a preference ordering over the available alternatives at a point in time, therefore, the notion that the “preferences” of the “state” are stable over time, or that they obey potentially important regularity assumptions, may be quite problematic. Although one must acknowledge this problem, there is often little to be done about it in a tractable modeling framework beyond remaining attentive to its possible