The US dollar currently has a dominant – albeit not exclusive – role for invoicing of international trade flows. We contrast how economic fundamentals and policy actions impact this pattern drawing on an extensive multi-country database. In terms of economic fundamentals, the weight of a region in international trade supports use of its currency. Trade to the United States or the Euro area is more invoiced in dollars and euros respectively, as is trade to countries that peg to these major currencies. Exporters in more homogenous sectors coalesce on similar invoicing choices, which solely benefits the dollar. We assess the role of policy through the impact of renminbi swap lines set by some countries with the People’s Bank of China. Focusing on a subsample for which we have information on renminbi use, we find that swap lines promote it in countries which trade extensively with China. This occurs primarily at the expense of the dollar, and to a lesser extent, the euro.