coin, piece of metal, usually a disk of gold, silver, nickel, bronze, copper, aluminum, or a combination of such metals, stamped by authority of a government as a guarantee of its real or exchange value and used as money. Coinage was probably invented independently in Lydia or in the Aegean Islands and in China before 700 B.C. The earliest known example is an electrum coin (c.700 B.C.) of Lydia. The first U.S. mint was established in 1792. Mottoes used on many U.S. coins are "E Pluribus Unum" (1795) and "In God We Trust" (1864). Early coins were die-struck by hand and showed many individual variations. Standardized coins date from the use of a mill and screw machine (invented c.1561). Coins are usually stamped from rolled metal blanks, then milled. The final product bears a design impressed upon it between the upper and lower dies of a coining press. Milled or lettered edges have been used since the 17th cent. to discourage the removal of slivers of metal, especially from gold or silver coins. No gold coins have circulated in the United States since 1934, when the domestic gold standard was abandoned. Until 1965, silver was used in the minting of dimes and quarters, but by the 1980s silver had disappeared from American coinage altogether. In the mid-1990s, the European Union developed a common currency for its members. The new currency, called the euro, was inaugurated in 1999; coins and notes went into circulation in 2002, replacing the currencies of most EU members (see European Monetary System). Canada introduced the first colored coin for circulation in 2004; it was a quarter featuring a poppy. See also numismatics.

Systematic accumulation and study of coins, tokens, paper money, and objects of similar form and purpose. The long-held view that coin collecting began with the Italian Renaissance has been challenged by growing evidence that the activity is far more venerable. There exist a variety of literary accounts of collecting from ancient Greek and Roman sources, and there is tangible archaeological evidence that coins have been collected at least from the Roman era. Collecting was perhaps less important during the Middle Ages, but during the 15th–16th centuries it again became more popular, mostly among European aristocrats. In the 17th century the nature of collecting shifted slowly toward serious research. As a result, very broad collections were formed, studied, and catalogued. In the 20th century museums took over the main task of forming large collections of great detail and range. It was also during this time that a popular market for coins began to develop. Previously only the very wealthy purchased ancient coins and the number of sources were few. London became the world's largest numismatic market, serving the interests of public collections and private collectors in many lands. The Internet became an important aspect of coin collecting in the late 1990s, both because it afforded a virtual marketplace that permitted buyers and sellers from anywhere in the world to trade in coins and for the educational effect of the many Web sites devoted to the hobby. Seealso philately.

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Certification of a piece of metal or other material (such as leather or porcelain) by a mark or marks upon it as being of a specific intrinsic or exchange value. Croesus (r. circa 560–546 BC) is generally credited with issuing the first official government coinage of certified purity and weight. Counterfeiting was widespread in the Middle Ages. In the late 15th century, equipment capable of providing coins of reliable weight and size was developed in Italy. The Industrial Revolution saw further refinements in coinage techniques. Most of the basic motifs of modern coinage were introduced in antiquity. In the Greek world, relief imprinting gradually replaced the roughly impressed reverse punch of the Lydians. Alexander the Great introduced the coin-portrait; these initially depicted gods or heroes and later living monarchs. Until the end of the 19th century, Chinese coins were cast much like those of the early Greeks; the square-holed Chinese bronze coins were issued in essentially the same size and shape for almost 2,500 years.

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