通货，是指在社会经济活动中作为流通手段的货币。货币的一个作为交换媒介形式的部分，通货是各国货币供应量中无需背书的部分，只包括纸币、硬币，不包括货币的存储功能以及其他支付手段。各国通货根据汇率在通货领域进行交换，由于不同的汇率而分为固定通货和浮动通货。各国一般都是控制自己本国通货的供需状态，唯一例外的是欧盟，由欧洲中央银行统一控制欧盟各国的通货政策。

各国由中央银行或财政部控制本国的通货，来调整经济状况，有的几个国家统一实行一种通货，有的国家允许外国通货在本国流通，但大部分国家发行自己本国的通货，并不允许外国通货在本国流通。在发达国家，由于支票和电子货币的大量使用，通货已经只占货币供应量中的小部分。

A currency (from Middle English:curraunt, "in circulation", from Latin:currens, -entis) in the most specific use of the word refers to money in any form when in actual use or circulation as a medium of exchange, especially circulating banknotes and coins. A more general definition is that a currency is a system of money (monetary units) in common use, especially in a nation. Under this definition, British pounds, U.S. dollars, and European euros are examples of currency. These various currencies are recognized stores of value, and are traded between nations in foreign exchange markets, which determine the relative values of the different currencies. Currencies in this sense are defined by governments, and each type has limited boundaries of acceptance.