贬值或货币贬值是指某一特定货币价值下降，此价值一般会以兑换为其他货币单位后的金额为准，意指价格下降或是价值减少。

贬值的反义词是升值，是指货币的价值上升。货币的升值或贬值会影响其在国际市场上的价值，也会反映在汇率上。

货币贬值和通货膨胀不同，通货膨胀是指某一特定通货可购买的商品或服务（即购买力）减少。

货币贬值后，需用较多的本国货币兑换等值外币，因此不利于进口，也会造成国内进口商品物价的上涨。不过对于商品出口而言，因为等值本国货币所对应的外币下降，对于出口有利。

Devaluation in modern monetary policy is a reduction in the value of a currency with respect to those goods, services or other monetary units with which that currency can be exchanged. "Devaluation" means official lowering of the value of a country's currency within a fixed exchange rate system, by which the monetary authority formally sets a new fixed rate with respect to a foreign reference currency. In contrast, depreciation is used to describe a decrease in a currency's value (relative to other major currency benchmarks) due to market forces, not government or central bank policy actions. Under the second system central banks maintain the rates up or down by buying or selling foreign currency, usually but not always USD. The opposite of devaluation is called revaluation.