A fine or mulct (the latter synonym typically used in civil law) is a penalty of money that a court of law or other authority decides has to be paid as punishment for a crime or other offense. The amount of a fine can be determined case by case, but it is often announced in advance.

The most usual use of the term is for financial punishments for the commission of crimes, especially minor crimes, or as the settlement of a claim.

One common example of a fine is money paid for violations of traffic laws. Currently in English common law, relatively small fines are used either in place of or alongside community service orders for low-level criminal offences. Larger fines are also given independently or alongside shorter prison sentences when the judge or magistrate considers a considerable amount of retribution is necessary, but there is unlikely to be significant danger to the public. For instance, fraud is often punished by very large fines since fraudsters are typically banned from the position or profession they abused to commit their crimes.

Fines can also be used as a form of tax. Money for bail may be applied toward a fine.

A day-fine is a fine that, above a minimum, is based on personal income (similar to progressive taxation), as opposed to a fine of a fixed amount. Day-fines are often implemented as a way to alleviate some of the burden on the poor, who might otherwise have issues paying/affording some fines.

Some fines are small, such as for loitering, for which fines (in the United States) range from about $25 to $100. In some areas of the United States (for example California, New York, Texas, and Washington D.C.), fines for petty crimes, such as criminal mischief (shouting in public places, projecting an object at a police car) range from $2,500 to $5,000.