The United States one-cent coin, commonly known as a penny, is a unit of currency equaling one one-hundredth of a United States dollar. The cent's symbol is ¢. Its obverse has featured the profile of President Abraham Lincoln since 1909, the centennial of his birth. From 1959 (the sesquicentennial of Lincoln's birth) to 2008, the reverse featured the Lincoln Memorial. Four different reverse designs in 2009 honored Lincoln's 200th birthday and a new, permanent reverse – the Union Shield – was introduced in 2010. The coin is 0.75 inches (19.05 mm) in diameter and 0.061 inches (1.55 mm) in thickness.

The U.S. Mint's official name for a penny is "cent" and the U.S. Treasury's official name is "one cent piece". The colloquial term penny derives from the British coin of the same name, the pre-decimal version of which had a similar value. In American English, pennies is the plural form, other plural forms pence and pee (standard use in British English) are not used.

As of 2012, it costs the U.S. Mint 2.00 cents to make a cent because of the cost of materials and production. This figure includes the Mint’s fixed components for distribution and fabrication, estimated at $13 million in FY 2011. It also includes Mint overhead allocated to the penny, which was $17.7 million for 2011. Fixed costs and overhead would have to be absorbed by other circulating coins without the penny. The loss in profitability due to producing the one cent coin in the United States for the year of 2012 was $58,000,000. This was a slight decrease from 2011, the year before, which had a production loss of $60,200,000.

In honor of the Lincoln cent's 100th anniversary, special 2009 cents were minted for collectors in the same composition as the 1909 coins.

The isotope composition of early coins spanning the period of 1828 to 1843 cents reflects that of copper from Cornwall ores from England while coins after 1850 that from the Keweenaw Peninsula, Michigan ores, a finding consistent with historical records.

In 1943, at the peak of World War II, zinc-coated steel cents were made for a short time because of war demands for copper. A few copper cents from 1943 were produced from the 1942 planchets remaining in the bins. Similarly, some 1944 steel cents have been confirmed. From 1944 through 1946, salvaged ammunition shells made their way into the minting process, and it was not uncommon to see coins featuring streaks of brass or having a considerably darker finish than other issues.

During the early 1970s, the price of copper rose to a point where the cent contained almost one cent's worth of copper. This led the Mint to test alternative metals, including aluminum and bronze-clad steel. Aluminum was chosen, and over 1.5 million of these pennies were struck and ready for public release before ultimately being rejected. The proposed aluminum pennies were rejected for two reasons: vending machine owners complained the coins would cause mechanical problems; and pediatricians and pediatric radiologists pointed out that the radiodensity of the metal inside the respiratory and gastrointestinal tracts was close to that of soft tissue, and the coins would therefore be difficult to detect in X-ray imaging. One aluminum cent was donated to the Smithsonian Institution.

The cent's composition was changed in 1982 because the value of the copper in the coin started to rise above one cent. This was mainly caused by inflation. Some 1982 pennies used the 97.5% zinc composition, while others used the 95% copper composition. With the exception of 2009 bicentennial cents minted specifically for collectors, United States cents minted after 1982 have been copper-plated zinc. Although this was initiated because of the cost of producing 95% copper cents, as of 2012, each cent costs approximately 2.00 cents for the mint to produce.

Distinguishing between the bronze and copper cents and the newer, zinc cents can be done by dropping the coin on a solid surface. The predominantly copper coins produce a higher-pitched ringing sound, while the zinc coins make a lower-pitched "clunk". In addition, a full 50-cent roll of pre-1982/3 coins weighs 5.4 oz compared to a post-1982–83 roll which weighs 4.4 oz.

When the Lincoln one-cent coin made its initial appearance in 1909, it marked a radical departure from the accepted styling of United States coinage, as it was the first regular coin to bear a portrait other than the mythical Liberty, which appeared on most pre-1909 regular coins. (Even the so-called Indian Head of the Indian Head cent it replaced depicted Liberty as a Native American. The Sacagawea dollar depicts a historical person, and is the first U.S. circulation coin to honor a specific Native person, although there are no known portraits of Sacagawea. The Indian Head nickel depicts an idealized Indian chief rather than a specific person.) Previously, a strong feeling had prevailed against using portraits on coins in the United States, but public sentiment stemming from the 100th anniversary celebration of Abraham Lincoln's birth proved stronger than the long-standing tradition.

A variety of privately minted tokens bearing Lincoln's image circulated as one-cent pieces during Lincoln's presidency; legitimate coinage had become scarce during the Civil War. These early tokens undoubtedly influenced the denomination, appearance, size, and composition of Lincoln cents.

Theodore Roosevelt, the 26th US President, thought American coins were so common and uninspiring that he attempted to get the motto "In God We Trust" removed as offending religion. Roosevelt had the opportunity to pose for a young Lithuanian-born Jew, Victor David Brenner, who, since arriving nineteen years earlier in the United States had become one of the nation’s premier medalists. Roosevelt had learned of Brenner's talents in a settlement house on New York City's Lower East Side and was immediately impressed with a bas-relief that Brenner had made of Lincoln, based on a Mathew Brady photograph. Roosevelt, who considered Lincoln the savior of the Union and the greatest Republican President and who also considered himself Lincoln’s political heir, ordered the new Lincoln cent to be based on Brenner's work and that it go just in time to commemorate Lincoln’s 100th birthday in 1909. The likeness of President Lincoln on the obverse of the coin is an adaptation of a plaque Brenner executed several years earlier and which had come to the attention of President Roosevelt in New York.

In addition to the prescribed elements on U.S. coins – LIBERTY and the date – the motto In God We Trust appeared for the first time on a coin of this denomination. Of interest also is the fact that the United States Congress passed the Act of March 3, 1865, authorizing the use of this motto on U.S. coins[citation needed], during Lincoln's tenure in office.

Even though no legislation was required for the new design, approval of the Secretary of the Treasury was necessary to make the change. Franklin MacVeagh gave his approval on July 14, 1909, and not quite three weeks later, on August 2, the new coin was released to the public.