The guinea is a coin that was minted in the Kingdom of England and later in the Kingdom of Great Britain and the United Kingdom between 1663 and 1813. It was the first English machine-struck gold coin, originally worth one pound sterling, equal to twenty shillings; but rises in the price of gold caused the value of the guinea to increase, at times to as high as thirty shillings; from 1717 until 1816, its value was officially fixed at twenty-one shillings. Following that, Great Britain adopted the gold standard and guinea became a colloquial term.

The name came from the Guinea region in West Africa, where much of the gold used to make the coins originated. Although no longer circulated, the term guinea survives in some circles, notably horse racing, and in the sale of rams, to mean an amount of one pound and one shilling (21 shillings) or one pound and five pence in decimalised currency. The name also forms the basis for the Arabic word for the Egyptian pound الجنيه el-Gineih, as a sum of 100 qurush (i.e., one pound) was worth approximately 21 shillings at the end of the 19th century.