比较优势（比较利益）或相对优势是经济学的概念，解释了为何在拥有较的机会成本的优势下生产，贸易对双方都有利。可分为静态比较优势和动态比较优势。当一方（一个人，一间公司，或一国）进行一项生产时所付出的机会成本比另一方低，这一方面拥有了进行这项生产的比较优势。

例如甲国和乙国都只生产衣服和食物，在同质的资源下，甲国生产一单位衣服的机会成本是二单位食物，而乙国生产一单位衣服的机会成本是三单位食物，根据比较优势理论，甲国享有生产衣服的比较优势，便应该专业生产衣服，并出口之，以换取食物。而乙国在生产衣服上有比较劣势，意味它生产食物享有比较优势。没有任何一方在所有物品的生产上均享有比较优势，所以比较优势的本质是互利的。

The theory of comparative advantage is an economic theory about the work gains from trade for individuals, firms, or nations that arise from differences in their factor endowments or technological progress. In an economic model, an agent has a comparative advantage over another in producing a particular good if they can produce that good at a lower relative opportunity cost or autarky price, i.e. at a lower relative marginal cost prior to trade. One does not compare the monetary costs of production or even the resource costs (labor needed per unit of output) of production. Instead, one must compare the opportunity costs of producing goods across countries. The closely related law or principle of comparative advantage holds that under free trade, an agent will produce more of and consume less of a good for which they have a comparative advantage.