Trade dollars were silver coins minted as trade coins by various countries to facilitate trade with countries in East Asia, especially China and Japan. They all approximated in weight and fineness to the Spanish dollar, which had set the standard for a de facto common currency for trade in the Far East.

The Spanish dollar, also known as the piece of eight, is a silver coin of approximately 38 mm (1.5 in) diameter worth eight Spanish reales. It was minted in the Spanish Empire following a monetary reform in 1497 with content 25.563 g (0.8219 ozt) fine silver. It was widely used as the first international currency because of its uniformity in standard and milling characteristics. Some countries countermarked the Spanish dollar so it could be used as their local currency.