Kenneth W. Abbott et al. define legalization as aiming to provide “identifiable dimensions of variation whose effects on international behavior can be empirically explored” (p. 19). It revolves around three characteristics that international institutions may or may not display. “Obligation” means that states are “legally bound by a rule of commitment in the sense that their behavior thereunder is subject to scrutiny under the general rules, procedures and discourse of international law, and often of domestic law” (p. 17). “Precision” is a feature of rules that “unambiguously define the conduct they require, authorize or proscribe” (p. 17). “Delegation” provides third parties with “authority to implement, interpret and apply the rules; to resolve disputes; and (possibly) make further rules” (p. 17). Each characteristic can vary independently. Legalization “encompasses a multidimensional continuum” (p. 17), ranging from full legalization, to harder or softer forms of legalization (with different degrees and combinations of obligation, precision, and delegation), to complete absence of legalization.

For the framers of the volume, international law and politics exist in a reciprocal relationship, with one impacting on the other. In suggesting that institutions mediate this relationship, the legalization project declares its theoretical provenance: Legalization is a particular form of institutionalization. The introduction by Judith Goldstein et al. emphasizes, however, that the project's intent is “neither to praise nor to bury legalization, but to analyze its dimensions, its sources, and its current and prospective effects” (p. 15). The volume compiles contributions that begin this analytical work. Kenneth W. Abbott and Duncan Snidal examine harder and softer legal arrangements and the differing costs and benefits they produce. Robert O. Keohane, Andrew Moravcsik, and Anne-Marie Slaughter focus on “delegation,” notably, the implications of various interstate and transnational third-party dispute resolution models. The other contributions explore legalization in different settings. Three regional case studies focus on legalization in the European Union (Karen J. Alter); the North American Free Trade Agreement (Frederick M. Abbott); and in Asia-Pacific regional institutions (Miles Kahler). Three issue-oriented case studies examine the role of legalization in international monetary affairs (Beth A. Simmons); the interaction between legalization, trade liberalization, and domestic politics (Judith Goldstein and Lisa L. Martin); and the impact of legalization on human rights law and practice in Latin America (Ellen L. Lutz and Kathryn Sikkink).

To map out common conceptual ground on a topic notorious for deep theoretical divisions between and within the disciplines of IR and IL is daunting, to say the least. Legalization and World Politics deserves praise for the effort to chart a possible course for interdisciplinary exchange and collaboration. Yet, readers in both disciplines should be alert to the fact that the conceptual bridges built in Legalization have the potential to extend and to narrow, to guide and to mislead, to focus and to obscure the undertaking. As the framers themselves stress, legalization is not international law. IR and IL scholars must pay close attention to this fact and its implications, lest they risk talking past one another, undermining the important bridge–building goal of the legalization project.

IR theorists should note that the concept of legalization casts a particular image of international law. The focus is on structural manifestations of law: textual expressions of greater or lesser obligation, more or less precision; institutions that apply international law in more or less formal ways. Thus, for all its emphasis on the potential value of diverse forms of legalization, the project's vision of international law is a narrow one. And although the framers' declared goal is to decouple international law and enforcement, some of the volume's contributions seem to conflate obligation and enforceability (Alter), or (political) bindingness and enforcement (Goldstein and Martin). At the very least, this blurring points to the potential for misunderstanding legalization's indicators.

Given its institutionalist roots, it may not be surprising that Legalization's focus is on regulatory regimes and treaties. Nonetheless, it is striking that virtually no attention is paid to some of the most important threads in the fabric of international law. Where do customary norms fit into the legalization framework? They may be obligatory within its terms, but they are often not precise or subject to significant delegation. Is one to conclude that most customary international law is weakly legalized? What would that mean? The example of customary law illustrates how Legalization's focus on structures and hierarchical forms of application distracts attention from at least some of what enables international law to operate in its still predominantly horizontal setting. By employing a thin definition of legal obligation, Legalization's framers may avoid the pitfalls of theoretical disagreements regarding the essence of legal obligation. But they may also obscure important insights into what makes legal obligation distinctive. A closely related blind spot of the legalization framework concerns legitimacy, of both substance and processes of international law. To many international lawyers, legitimacy is central to explaining international law's ability to influence in the absence of coercion. Legalization scholars, too, should be interested in legitimacy—it may well be crucial in linking obligation, precision, and delegation. It may help explain progression toward greater legalization, or when legalization is most likely to affect actor behavior.

IL scholars, in turn, should be aware of the assumptions that underpin the institutionalist theory from which the legalization concept derives. One core assumption is that actors make rational choices about utility maximizing forms of institutionalization or legalization. Thus, it is no surprise that the majority of contributions conclude that the degree, form, and impact of legalization are affected by assessments of anticipated costs and benefits by state and nonstate actors. Such assessments are undoubtedly important and deserve the careful attention they receive in Legalization. This is especially true in the economic realm, on which all but one of the volume's case studies focus. But surely rational assessment is not the whole story of international law's influence (nor, for that matter, of politics). Normative factors matter, too.

As constructivist IR scholarship illustrates, norms have the capacity to shape not only actors' perceptions of their interests but also how they understand themselves and their position in the world. The framers of Legalization acknowledge the relevance of international norms. Indeed, Abbott and Snidal's exploration of hard and soft legalization stresses repeatedly that legal norms not only affect material incentives but also operate by “modifying understandings, standards of behavior, and identities” (p. 41). Yet, the analysis in Legalization remains largely interest based. Only one contribution, by Lutz and Sikkink, is norm focused. They suggest that human rights norms significantly altered the behavior of Latin American states, and that this impact was unrelated to the degree to which the relevant norms were legalized. Their case study illustrates that legal norms can emerge and exert influence in absence of, even despite, perceived self-interests of states. These conclusions stand in stark contrast to the tenor of the rest of the volume and challenge the assumption that actors ‘choose' forms of legalization. This may explain why, in the volume's concluding essay, Miles Kahler suggests that Lutz and Sikkink's “explanation has its own shortcomings,” most notably that “normative consensus is difficult to test outside the behavioral changes” that are attributed to it (p. 294). His comments reveal that the heuristic bridges built by Legalization remain fragile even within the discipline of IR. The volume might have been able to shed more light on the underlying questions had it contained more case studies from outside of the economic field.

Legalization and World Politics is an impressive volume with high-quality contributions. This is not a collection of essays loosely stitched around a common theme. The conceptualization and approach of the volume grew from several years of exchange among a core group of contributors. IR and IL scholars alike should take the book as an invitation to test the strengths of the legalization concept and to expose its shortcomings. Both types of responses are crucial to furthering fruitful collaboration between the two disciplines, and our understanding of the role of international law in international affairs.