Following the terrorist attacks of September 11, 2001, U.S. policymakers and their international counterparts quickly devised new programs for protecting seaports and the maritime supply chain. This paper focuses on one such program, the U.S. Container Security Initiative, which screens and...

What are the barriers that separate nations; While recent work provides intriguing clues, we have remarkably little concrete evidence as to the nature, size, and shape of barriers. This paper offers direct and indirect evidence on trade barriers, moving us toward a comprehensive geography of...

We collect extensive data on worldwide trade by transportation mode and use this to provide detailed comparisons of the greenhouse gas emissions associated with output versus international transportation of traded goods. International transport is responsible for 33 percent of world-wide...

Not surprisingly, big countries trade more than small countries. In this paper we use data on shipments by 110 exporters to 59 importers in 5,000 product categories to ask: how? Do big countries trade larger quantities of a common set of goods (the intensive margin), a larger set of goods (the...

In this paper we examine whether a generalized version of Flam and Helpman's (1987) model of vertical differentiation can reconcile three facts. One, countries import only a subset of available varieties. Two, import prices vary across exporters within narrow product categories. Three, US growth...