Decimalization refers to any process of converting from traditional units, usually of money, to a decimal system.

This process has been undergone by all countries except Mauritania and Saudi Arabia, but the former has in practice dropped their smaller unit since it is worth so little, and the latter is currently phasing out their non-decimal unit by not minting any new coins in it.

France decimalised first, abandoning the Livre tournois at the time of the Revolution, and imposed decimalisation on a number of countries that it invaded at that time. The United States introduced a decimal currency after achieving independence from Britain. However, many Commonwealth countries retained traditional money systems (pounds, shillings & pence) after achieving effective independence as Dominions, and only decimalised in the second half of the 20th century.

South Africa decimalised in 1961, introducing the rand as the new unit of currency. When Australia decimalised in 1966, the new Australian dollar was fixed at ten shillings (i.e. half an Australian pound). A similar strategy was followed in New Zealand in 1967, with the introduction of the New Zealand dollar.

The United Kingdom and the Republic of Ireland decimalised the Pound Sterling and the Irish pound on Decimal Day, 15 February 1971.

Many other former British colonies, such as Singapore, Malaya, Sri Lanka, Mauritius, and the Seychelles used decimal currencies, even while under British rule.

India changed from the Rupee, Anna, Pie system to decimal currency in 1957. Pakistan followed in 1961. Sri Lanka (formerly Ceylon) has used a decimal currency since 1869.

In France, decimalisation of the coinage was accompanied by metrication of other measures. However, in general the two have not gone hand in hand: the U.S. has never metricated, Canada has only recently done so despite having long had a decimal coinage, and the U.K. has only metricated to a limited extent.