This paper examines the question of whether a country's exchange rate policy choices are influenced by membership in preferential trade agreements (PTAs). We argue that PTAs, by constraining a government's ability to employ trade protection, increase its incentives to maintain monetary and fiscal autonomy in order to manipulate the domestic political economy. Consequently, we contend that countries are less likely to adopt or sustain a fixed exchange rate when they have signed a PTA with their “base” country—the country to whom they have traditionally fixed the currency or the major industrial country to whom they have the most extensive trade ties. Likewise, countries that have signed a “base” PTA also tend to have more depreciated/undervalued currencies, as measured by the level of the real exchange rate. Using data on 99 countries from 1975 to 2004, we find strong support for these hypotheses. These findings shed light on the complex relationship between different types of macroeconomic policies in the contemporary world economy. More broadly, they speak to the question of whether international agreements are credible commitment mechanisms when close policy substitutes exist at the domestic level.