本文使用搜尋模型探討生產效率如何影響一國貨幣的國際地位，以及國際通貨發行國貨幣政策的效果。當一國市場規模夠大且通膨率低，該國生產力提高有助於其貨幣成為國際通貨。美國作為國際通貨發行國，若生產力高於他國，美元通膨上升將使兩國福利降低，且美國福利受損程度較大，兩國福利差距縮小。他國因生產劣勢使其境內生產者福利遠低於消費者，美國通膨政策將使他國消費者支付更多鑄幣稅，縮小其與生產者的福利差距。若他國生產力較美國高，則美元通膨上升反而擴大兩國福利差距，也惡化了他國境內的福利分配。因此，美國實施寬鬆貨幣政策對其他國家的影響將視其他國家與美國生產力差異程度而定。

We construct a two-country two-currency search monetary model to study how improved productivity in a country affects the circulation of its currency, and the monetary policy implications. Increased productivity in a country helps its currency circulate internationally, and this is more likely to occur if its market size is large and inflation rate is low. If the issuer of the international currency (e.g., the U.S.) has higher productivity, it enjoys higher welfare than the other country. In the local currency issuing country, the welfare of its producers is lower than that of consumers, due to the productivity disadvantage. Higher inflation of the international currency results in different impacts between countries, and across different types of agents in the other country: First, it reduces welfare in both countries, with the international currency issuing country suffering higher welfare loss; second, it hurts consumers more than producers in the other country, and thereby reduces the welfare differential, because consumers need to pay more seigniorage taxes. If the local currency issuing country has higher productivity, it enjoys higher welfare than the international currency issuer. Higher inflation of the international currency thus increases welfare differences between the two countries, and also worsens the distribution of welfare in the other country. Monetary policy implications thus depend on heterogeneity in productivity.