section uses tariffs to provide a first round of answers to each of our five major questions: Do some countries have lower tariffs than others? Within countries, which sectors receive the most tariff protection? How do tariffs change over time? Do countries set tariffs so as to discriminate among their trading partners? Finally, how liberalized are tariffs?

Much of our formal analysis in this section relies on cross-country and inter-temporal data comparisons where, for reasons of data quality, we do not attempt to be comprehensive. Instead, we focus on a sample of 31 economies listed in Table 1.<sup>6</sup> These major economies were not chosen randomly - they include the Group of 20 (G20) economies plus an additional set of developing countries each with 2013 populations of over 40 million. Collectively in 2013, these 31 economies represented 83 percent of the world’s population, 91 percent of GDP, 80 percent of imports, and 79 percent of exports. Figure 1 illustrates their geographic diversity.<sup>7</sup> We begin in Section 2.1 by introducing and describing _ad valorem_ import tariffs under the WTO. In the contemporary data, we find the tariffs that countries apply are relatively low on average. However, for many countries, these applied tariffs are substantially lower than the maximum tariffs allowed under the WTO, implying that trade is much less liberalized when viewed through the lens of the tariffs that countries are legally permitted to apply. There are also surprisingly large differences across countries in the average level of tariffs: high income countries have more liberal trade regimes than middle income countries which, in turn, have more liberal regimes than low income countries. Across the board, countries tend to charge higher tariffs in the agricultural sector, in manufacturing industries such as textiles, apparel, and footwear, and in final goods relative to intermediate inputs. Finally, over the most recent twenty year period (1993-2013), we find a general downward trend in tariffs for many, but not all, countries. Furthermore, while applied tariffs for high income countries exhibit little variation at the annual frequency over the period, there is slightly more variation for lower-income countries.

In Section 2.2, we document the frequency with which countries apply specific duties, or per unit import tariffs, under the WTO. These sorts of tariffs arise disproportionately in a number of high and middle-income economies and are mostly limited to sectors such as agriculture, textiles and apparel, and footwear. We then motivate why it is important to consider specific duties distinctly from ad valorem tariffs. The ad valorem equivalent of a specific duty can vary - either over time or with respect to its discriminatory effect across trading partners - in ways that are distinctive from tariffs applied in ad valorem form.

> 6Here and throughout we refer to economies and countries interchangeably even though we will generally rely on information about the European Union collectively as opposed to its member states individually. Since these countries have a common trade policy set by the European Commission, we treat them as one economy. The 28 member countries of the EU as of 2013 included Austria, Belgium, Bulgaria, Croatia, Republic of Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden and the UK.

> 7Sub-Saharan Africa is under-represented in the sample of 31 economies utilized in the empirical analysis. Nevertheless, the tariff characteristics for African countries more generally, and that we detail below, are well captured by the countries included in the analysis, and especially Democratic Republic of Congo, Ethiopia (a WTO nonmember), Kenya, Nigeria, and Tanzania. Bown (2015) provides additional descriptive analysis of the tariffs for developing countries, including African countries.

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