Instead, our specific approach is to characterize the contemporary landscape of BTB policies through a survey of case studies of particularly contentious domestic policies that have been the subject of formal WTO disputes. While the case studies are not comprehensive, they are arguably representative of the BTB policies most frequently challenged under the WTO. They cover roughly 50 formal WTO disputes over BTB policies, or 10 percent of the population of all WTO disputes arising between 1995 and 2015.<sup>92</sup> And for most of the case studies on BTB policies, we are able to explicitly direct the interested reader to additional research from a now established and growing literature whereby economists have been paired with legal scholars to provide a jointly-written, detailed analyses of the domestic policies, markets, and jurisprudence arising under the individual WTO dispute.<sup>93</sup> The tables in each of the four subsections below provide explicit references to the published dispute-specific introductions to the policies and the more detailed analyses.

By introducing these conflicts over BTB policies, we demonstrate that next major area for the world trading system involves confronting the balance of respecting local preferences, internalizing cross-border policy externalities that arise through trade, and yet integrating economic activity across borders so as to make the most productive use of global resources. And yet not surprisingly, our main result from this section is that much more theoretical, empirical, and quantitative research is needed before we can systematically characterize in any meaningful way the trade restrictiveness, or levels of import protection, associated with BTB policies. Our discussion tends to disproportionately feature BTB policies that high income economies impose and that are potentially affecting trade in major sectors of interest to these economies, such as aircraft, semiconductors, clean energy, autos, agriculture, foodstuffs, and also cigarettes and alcohol.<sup>94</sup> While these features may motivate BTB policies as worthy of additional research scrutiny, we must caveat that one should not conclude that import protection through BTB policies is thus more likely to arise in these particular countries and sectors. In a final section below, we return to these and other caveats regarding the interpretation of these results given sample selection bias due to the endogeneity of the dispute settlement process, as well as how the trade restrictiveness of BTB policies also interacts with levels of import protection through border barriers.

defined categories of non-tariff measures (NTMs). These NTMs are then also mapped to HS06 products based on the descriptions of the products mentioned in the laws and regulations. While such efforts at data collection and construction are surely a step in the right direction, other significant efforts will be required before these data can be used to address the main questions of this chapter.

> 92For context, the temporary trade barriers (antidumping, countervailing, and safeguards) described in Section 3.1 were the most frequently disputed border policy during the period. Applied TTBs were the topic of more than 175 disputes - i.e., more than 35 percent of all WTO disputes (Bown, 2014a.)

> 93Beginning in 2001, in a project initially sponsored by the American Law Institute, Henrik Horn and Petros Mavroidis initiated a program that annually convened a set of economists and legal scholars so as to provide reports assessing the new case law arising from the WTO’s Appellate Body (and unappealed Panel Reports). These joint assessments have subsequently been published annually by Cambridge University Press, primarily through special issues of the _World Trade Review_ . In 2011, one of the co-authors of this chapter (Bown) took over co-directing the project (from Horn) with Mavroidis. After more than 15 years, the result is a body of work covering more than 100 WTO legal decisions.

> 94In their survey of all border and BTB policies subject to WTO disputes over 1995-2011, Bown and Reynolds (2015) find that WTO disputes collectively investigated nearly $1 trillion in goods imports, an average of $55 billion per year, or roughly 0.5 percent of world imports in 2011.

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