that are incurred not in the simple game in which defection is contemplated but in al Traditional international law scholars will find little solace in the reputational interpretation of opinio juris, however, because concern for reputation is no less self- interested than concern for payoffs in a narrower strategic interaction. Further, reputational considerations may be of minimal significance as a practical matter in many settings as both Goldsmith and Posner and Guzman argue. This general issue receives further attention below Aside from its examination of opinio juris, the law and economics literature makes a number of other useful points about the role of customary law. The commentators seem to agree that the ability of customary international law to orchestrate cooperation is limited to narrow circumstances. Problems that require complicated solutions are unlikely to be solved by implicit cooperation express negotiation and communication will probably be necessary. Further, problems that require the simultaneous cooperation of large numbers of nations will also be difficult to solve because of free rider problems in the enforcement mechanism. Even when a practice appears "customary"on a global scale, therefore, and is thought to represent mutual hat it is usuall than a recurring regul bilateral interaction Guzman makes the further point that if reputation is what creates some"force of law, then there is no reason to limit our conception of" to customary international law and treaties. Reputational concerns may be quite important to a world leader who gives her word to another, whether or not it is done in any formal fashion and whether or not it concerns some practice that is widespread in the international community. The raditional line between"hard law"(binding treaties and customary law) on the one hand and"soft law"(such as informal agreements and statements of intention) on the other may thus be quite misleading. Depending on context, states may be considerably more likely to comply with soft law than with hard law, and there is no reason to think that hard law is always preferable for orchestrating cooperation In short, economic thinking about customary international law calls into question the very meaning of the concept. It suggests that practices termed"lawin various interaction between states facing similar problems. The codification of customary law merely serves to publicize focal points, and to write down the rules of any game to facilitate future adherence to them. The capacity of customary"law to solve important problems that require cooperation or coordination is quite limited, and will tend to bethat are incurred not in the simple game in which defection is contemplated but in all other games where reputation affects the strategies played by other states. Traditional international law scholars will find little solace in the reputational interpretation of opinio juris, however, because concern for reputation is no less self￾interested than concern for payoffs in a narrower strategic interaction. Further, reputational considerations may be of minimal significance as a practical matter in many settings as both Goldsmith and Posner and Guzman argue. This general issue receives further attention below. Aside from its examination of opinio juris, the law and economics literature makes a number of other useful points about the role of customary law. The commentators seem to agree that the ability of customary international law to orchestrate cooperation is limited to narrow circumstances. Problems that require complicated solutions are unlikely to be solved by implicit cooperation—express negotiation and communication will probably be necessary. Further, problems that require the simultaneous cooperation of large numbers of nations will also be difficult to solve because of free rider problems in the enforcement mechanism. Even when a practice appears “customary” on a global scale, therefore, and is thought to represent mutual cooperation, the suggestion is that it is usually no more than a recurring regularity of bilateral interaction. Guzman makes the further point that if reputation is what creates some “force of law,” then there is no reason to limit our conception of “law” to customary international law and treaties. Reputational concerns may be quite important to a world leader who gives her word to another, whether or not it is done in any formal fashion and whether or not it concerns some practice that is widespread in the international community. The traditional line between “hard law” (binding treaties and customary law) on the one hand and “soft law” (such as informal agreements and statements of intention) on the other may thus be quite misleading. Depending on context, states may be considerably more likely to comply with soft law than with hard law, and there is no reason to think that hard law is always preferable for orchestrating cooperation. In short, economic thinking about customary international law calls into question the very meaning of the concept. It suggests that practices termed “law” in various quarters are no more that behavioral regularities that emerge from self-interested interaction between states facing similar problems. The codification of customary law merely serves to publicize focal points, and to write down the rules of any game to facilitate future adherence to them. The capacity of customary “law” to solve important problems that require cooperation or coordination is quite limited, and will tend to be