A large class of models with CES utility and iceberg trade costs are now known to generate isomorphic “gravity equations.” Economic interpretations of these gravity equations vary in terms of two basic elements: the exporter's “mass” variable and the elasticity of trade with respect to...

The large reduction in tariff rates worldwide under several rounds of the GATT is commonly credited with being one of the most notable economic policy accomplishments since World War II. However, the remarkable progress towards free trade of goods is unparalleled in trade with services where...