The ever-increasing exchange of goods and ideas among nations, as well as cross-border pollution, global warming, and international crime, pose urgent questions for international law. Here, two respected scholars provide an intellectual framework for assessing these pressing legal problems from a rational choice perspective.

The approach assumes that states are rational, forward-looking agents which use international law to address the actions of other states that may have consequences for their own citizens, and to obtain the benefits of international cooperation. It further assumes that in the absence of a central enforcement agency—that is, a world government—international law must be self-enforcing. States must believe that if they violate international agreements, other states will retaliate.

Consequently, Eric A. Posner and Alan O. Sykes devote considerable attention to the challenges of enforcing international law, which begin with the difficulties of determining what it is. In the absence of an international constitution, the sources for international law are vague. Lawyers must rely on statements contained in all manner of official documents and on simple observation of states’ behavior. This looseness leads international institutions such as the United Nations to deliver conflicting interpretations of the law’s most basic principles. The authors describe the conditions under which international law succeeds or fails, across a wide range of issues, including war crimes, human rights, international criminal law, principles of state responsibility, law of the sea, international trade regulation, and international investment law.

What is the role of law in a society in which order is maintained mostly through social norms, trust, and nonlegal sanctions? Eric Posner argues that social norms are sometimes desirable yet sometimes odious, and that the law is critical to enhancing good social norms and undermining bad ones. But he also argues that the proper regulation of social norms is a delicate and complex task, and that current understanding of social norms is inadequate for guiding judges and lawmakers. What is needed, and what this book offers, is a model of the relationship between law and social norms. The model shows that people's concern with establishing cooperative relationships leads them to engage in certain kinds of imitative behavior. The resulting behavioral patterns are called social norms.

Posner applies the model to several areas of law that involve the regulation of social norms, including laws governing gift-giving and nonprofit organizations; family law; criminal law; laws governing speech, voting, and discrimination; and contract law. Among the engaging questions posed are: Would the legalization of gay marriage harm traditional married couples? Is it beneficial to shame criminals? Why should the law reward those who make charitable contributions? Would people vote more if non-voters were penalized? The author approaches these questions using the tools of game theory, but his arguments are simply stated and make no technical demands on the reader.

Cost-benefit analysis (CBA) has been an important policy tool of government since the 1980s, when the Reagan administration ordered that all major new regulations be subjected to a rigorous test of whether their projected benefits would outweigh their costs. Not surprisingly, CBA has been criticized by many who claim that it neglects, especially on the benefit side, important values that are hard to measure.

In this book, the authors reconceptualize cost-benefit analysis, arguing that its objective should be overall well-being rather than economic efficiency. They show why the link between preferences and well-being is more complicated than economists have thought. Satisfying a person's preference for some outcome is welfare-enhancing only if he or she is self-interested and well-informed. Also, cost-benefit analysis is not a super-procedure but simply a way to identify welfare-maximizing policies. A separate kind of analysis is required to weigh rights and equal treatment.

This book not only places cost-benefit analysis on a firmer theoretical foundation, but also has many practical implications for how government agencies should undertake cost-benefit studies.