In economics, David Ricardo is credited for the principle of comparative advantage to explain how it can be beneficial for two parties (countries, regions, individuals and so on) to trade if one has a lower relative cost of producing some good. What matters is not the absolute cost of production but the opportunity cost, which measures how much production of one good is reduced to produce one more unit of the other good. Comparative advantage is a key economic concept in the study of free trade.

Under the principle of absolute advantage, developed by Adam Smith, one country can produce more output per unit of productive input than another. With comparative advantage, even if one country has an absolute advantage in every type of output, the disadvantaged country can benefit from specializing in and exporting the product(s) with the largest opportunity cost for the other country.