辅币，即辅助货币，是本位币单位以下的小额货币，主要用来辅助大面额货币的流通，供日常零星交易或找零之用，通常以小数点形式计数；汇率较高的货币多半拥有辅币，如一角、一分等币别。

辅币一般多为金属铸造的硬币，也有些纸制的纸币。

辅币一般是有限法偿货币。也有一些国家规定辅币为无限法偿货币，如中国大陆。 ****早年依新台币辅币发行办法限制辅币法偿，1955年删除该条例后已无法偿限制。

通常铸有辅币的国家，其币值都较高，但亦有例外，如日圆本身都有辅币。

Fractional currency, also referred to as shinplasters, was introduced by the United States federal government following the outbreak of the Civil War. These fractional notes were in use between 21 August 1862 and 15 February 1876, and issued in 3, 5, 10, 15, 25, and 50 cent denominations across five issuing periods. The complete type set below is part of the National Numismatic Collection, housed at the National Museum of American History, part of the Smithsonian Institution.