假币、伪钞，指伪造的货币，包括假钞票和硬币。

制造假币最原始的方法是用高解像度扫描仪扫描，再用工业打印机印出来，或用彩色复印机复印。有些伪钞配上金属线和假水印，增加像真度。但大多数的影像处理软件、扫描设备等会侦测钞票上的圆圈星座防伪技术等防伪记号以阻止伪钞制造。

但现今的伪钞制作技术，有些已达国家级的水准，甚至是政府开印钞厂复印外国假钞，利用照像与蚀刻制版，与分色印刷。也使每一张伪钞都有不同的编号。印刷伪钞用的油墨亦自真钞上采样，用高效液相层析仪找出相近的化学成份。

Counterfeit money is imitation currency produced without the legal sanction of the state or government. Producing or using counterfeit money is a form of fraud or forgery. Counterfeiting is almost as old as money itself. Plated copies (known as Fourrées) have been found of Lydian coins which are thought to be among the first western coins. Before the introduction of paper money, the most prevalent method of counterfeiting involved mixing base metals with pure gold or silver. A form of counterfeiting is the production of documents by legitimate printers in response to fraudulent instructions. During World War II, the Nazis forged British pounds and American dollars. Today some of the finest counterfeit banknotes are called Superdollars because of their high quality and likeness to the real US dollar. There has been significant counterfeiting of Euro banknotes and coins since the launch of the currency in 2002, but considerably less than for the US dollar.