This is the second post in my weekly NBER digest series.
Costinot and coauthors use the classic Melitz (2003) model of heterogeneous firms trade theory to derive optimal tax levels at the micro (firm) level. They find that optimal import taxes discriminate against the most profitable foreign exporters, while optimal export taxes are uniform across domestic exporters.
Relative to another recent paper by Costiinot, Donaldson, Vogel and Werning (2015), the assumption of monopolistic competition (rather than perfect competition) in this paper leads to conclusions that are exactly the opposite. More generally, this paper is part of the trend in international trade research to connect traditional macro theories to micro data regularities.
This is not a new topic, but De Loecker and Van Biesebroeck highlights two aspects that are not well addressed in previous research. First, the impact of international trade on market power and productive efficiency should be studied in an integrated framework. Second, trade liberalization has the potential to increase competition by enlarging the relevant market, but this effect is not well understood. The discussion on the relevant market definition in the trade context is especially insightful.