The mill or mille (₥) (sometimes mil in the UK, when discussing property taxes in the United States, or previously in Cyprus and Malta) is a now-abstract unit of currency used sometimes in accounting. In the United States, it is a notional unit equivalent to 1⁄1000 of a United States dollar (a tenth of a cent). In the United Kingdom it was proposed during the decades of discussion on the decimalization of the pound as a 1⁄1000 division of the pound sterling. Several other currencies used the mill, such as the Maltese lira.
United States 
The Coinage Act (1792) describes milles and other subdivisions of the dollar:
That the money of account of the United States shall be expressed in dollars or units, dismes or tenths, cents or hundredths, and milles or thousandths, a disme being the tenth part of a dollar, a cent the hundredth part of a dollar, a mille the thousandth part of a dollar, and that all accounts in the public offices and all proceedings in the courts of the United States shall be kept and had in conformity to this regulation.
The mint of Philadelphia made half cents worth 5 mills each from 1793 to 1857.
Tokens in this denomination were issued by some states and local governments (and by some private interests) for such uses as payment of sales tax. These were of inexpensive material such as tin, aluminum, plastic or paper. Rising inflation depreciated the value of these tokens in relation to the value of their constituent materials; this depreciation led to their eventual abandonment. (Virtually none were made after the 1960s.)
Today, most Americans would refer to fractions of a cent rather than mills, a term which is widely unknown. For example, a gasoline price of $3.019 per gallon, if pronounced in full, would be "three dollars (and) one and nine-tenths cents". Discount coupons, such as those for grocery items, usually include in their fine print a statement such as "Cash value less than 1⁄10 of 1 cent." There are also common occurrences of "half-cent" discounts on goods bought in quantity. However, the term "mill" is still used when discussing billing in the electric power industry as shorthand for the lengthier "1⁄1000 of a dollar per kilowatt hour". The term is also commonly used when discussing stock prices, the issuance of founder's stock of a company, and cigarette taxes.
Property tax 
Property taxes are also expressed in terms of mills per dollar assessed (a mill levy, known more widely in the US as a "mill rate"). For instance, with a millage rate of 5.753 mills, a $100,000 house would be taxed 575,300 mills, or $575.30. The term is often spelled "mil" when used in this context.
The term mill is often used in finance, particularly in conjunction with equity market microstructure, as one-hundredth of a cent. For example, a broker that charges 5 mils per share is taking in $5 every 1000 shares traded. Additionally, in finance the term is spelled "mil".
Mark Twain introduced a fictional elaboration of the mill in A Connecticut Yankee in King Arthur's Court. When Hank Morgan, the American time traveler, introduces decimal currency to Arthurian Britain, he has it denominated in cents, mills, and "milrays", or tenths of a mill (the name perhaps suggested by "myriad", meaning ten thousand or by the Portuguese and Brazilian milreis).
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Mills are or were formerly used in some cities to express property tax rates, in the same manner as in the U.S.
United Kingdom 
Proposed on several occasions as a division of the British pound under the "Pound and Mil" system, the mill was occasionally used in accounting. The 1862 report from the Select Committee on Weights and Measures noted that the Equitable Insurance Company had been keeping accounts in mills (rather than in shillings and pence) for such purposes for over 100 years. Such a unit of a thousandth of a pound would have been similar in value to the then-existing farthing coin (1⁄960 of a pound).
Maltese lira coinage included 2 mil, 3 mil, and 5 mil coins from 1972 to 1994, with 10 mils being equal to one cent. Prices could still be marked using mils until the country switched to the euro in 2008, however these were then rounded up for accounting purposes.
Republic of Rose Island 
Mandatory Palestine, Israel, Jordan 
The Palestine pound, used as the currency of the British Mandate for Palestine from 1927 to 1948, was divided into 1,000 mils. Its successor currencies, the Israeli lira and the Jordanian dinar, were also divided into 1⁄1000 units, respectively named the peruta and fils. The Israeli peruta lasted until 1960, and the Jordanian fils until 1992.
Hong Kong 
To this date 1, 2, and 5 millime (mills) are still in circulation, but they are no longer issued by the central bank. However larger coins such as the 10, 20, 50, and 100 millime coins are still in use and production.
Similar units 
- The Egyptian pound was formerly divided into 1000 milliemes, and 10 millimes equals 1 piaster.
- The Tunisian dinar is divided into 1000 millimes (10 millimes is the smallest currently-minted coin)
- The national currencies which are divided into 1000 fils are the Kuwaiti dinar (5 fils is the smallest currently-minted coin), Bahraini dinar (1 fill), Iraqi dinar (25 dinars). But as with the case of the United Arab Emirates dirham and the Yemeni rial, they are divided into 100 subunits.
- The Omani rial is divided into 1000 baisa.
- The Libyan dinar is divided into 1000 dirham since 1971.
- The Japanese yen was formerly divided into 100 sen or 1000 rin. An early proposed (but not accepted) design for the 1-rin coin used "1 mill" in the Romanized text
- Shorter Oxford English Dictionary, 6th Ed, Vol. 1, at 1782
- Journals of the Continental Congress, August 8, 1786
- U.S. Coinage Act of 1792
- "per mil symbol". Tech Target. Retrieved 2007-06-25.
- "SEC Market Structure Concept Release". Tradeworx, Inc. p. 5. Retrieved 2010-12-27.
- REPORT (1862) FROM THE SELECT COMMITTEE ON WEIGHTS AND MEASURES
- Ma Tak Wo 2004, Illustrated Catalogue of Hong Kong Currency, Ma Tak Wo Numismatic Co., LTD. Kowloon, Hong Kong.ISBN 962-85939-3-5