This article is about monetary coins. For other meanings see: Coin (disambiguation)

Coins, Banknotes, Forgery Collecting coins
In terms of its value as a collector's item, a coin is generally made more or less valuable by its condition, specific historial significance, rarity, quality/beauty of the design and general popularity with collectors. If a coin is deeply lacking in any of these, it is unlikely to be worth much. Bullion coins are also valued based on these factors, but are largely valued based on the value of the gold or silver in them.
Most coins nowadays are made of a base metal, and their value comes from their status as fiat money. This means that the value of the coin is decreed by government fiat (law), and thus is determined by the free market only as national currencies are subjected to arbitrage in international trade. This causes such coins to be monetary tokens in the same sense that paper currency is, when the paper currency is not backed directly by metal, but rather by a government guarantee of international exchange of goods or services. Some have suggested that such coins not be considered to be "true coins" (see below). However, because fiat money is backed by government guarantee of a certain amount of goods and services, where the value of this is in turn determined by free market currency arbitrage, similar to the case for the international arbitrage which determines the value of metals which back commodity money, in practice there is very little practical economic difference between the two types of money (types of currencies).
Sometimes, coins are minted that have fiat values lower than the value of their component metals, but this is never done intentionally and initially, and only happens by accident later in the history of coin production, as market values for the metal overtake the fiat declared face value of the coin. Examples of this phenomenon include the US nickel and US penny. As a result of the increase in the value of copper, the United States greatly reduced the amount of copper in each penny. Now, United States pennies are made up of zinc coated with copper. Extreme cases of large differences between fiat values and metal values of coins would cause coins to be removed from the market by illicit smelters interested in the value of their metal content. In fact, the United States Mint, in anticipation of this practice, implemented new interim rules on December 14, 2006, subject to public comment for 30 days, which criminalize the melting and export of pennies and nickels.[1] Violators can be punished with a fine of up to $10,000 and/or imprisoned for a maximum of five years.
To distinguish between these two types of coins, as well as from other forms of tokens which have been used as money, some monetary scholars have attempted to define by three criteria that an object must meet to be a "true coin". These criteria are:
It is believed by some scholars that the first coins (following the criteria above) were manufactured in Lydia, but apart from one example with the legend "I am the badge of Phales", these pieces have no writing on them, merely symbolic animals. Therefore it is pure guesswork to date the coins, and numismatists' only clue is that some were found buried under a temple from the early 6th Century BCE. Many great classical numismatists have debated whether these coins may have been struck (manufactured) under the authority of private individuals, although, as the coins get more common, it is certainly thought that some were made under King Croseus.
The first European coin to use Arabic numerals to date the year minted was the Swiss 1424 St. Gallen silver Plappart.

It must be made of a valuable material, and trade for close to the market value of that material.
It must be of a standardized weight and purity.
It must be marked to identify the authority that guarantees the content. The value of a coin
The question of the world's first coin has been, and still is debated. While it is believed by many that the Lydian Lion trite is the world's oldest coin, some argue that India's karshapanam is the world's first coin.

First coins

Main article: Debasement Coin debasement
The milled, or reeded, edges still found on many coins (always those that were once made of gold or silver, even if not so now) were originally designed to show that none of the valuable metal had been shaved off the coin. Prior to the use of milled edges, circulating coins commonly suffered from "shaving", by which unscrupulous persons would shave a small amount of precious metal from the edge. Unmilled British sterling silver coins were known to be shaved to almost half of their minted weight. This form of debasement in Tudor England led to the formulation of Gresham's Law. The monarch would have to periodically recall circulating coins, paying only bullion value of the silver, and re-mint them.
Traditionally, the side of a coin carrying a bust of a monarch or other authority, or a national emblem, is called the obverse, or colloquially, heads. The other side is called the reverse, or colloquially, tails. However, the rule is violated in some cases. [2] Another rule is that the side carrying the year of minting is the obverse, although some Chinese coins, most Canadian coins, the British 20p coin, and all Japanese coins, are an exception.
The orientation of the obverse with respect to the reverse differs between countries. Some coins have coin orientation, where the coin must be flipped vertically to see the other side; other coins, such as British coins, have medallic orientation, where the coin must be flipped horizontally to see the other side.
The exergue is the space on a coin beneath the main design, often used to show the coin's date, although it is sometimes left blank or containing a mintmark, privy mark, or some other decorative or informative design feature. Many coins do not have an exergue at all, and they are most common on coins with little or no legends such as the Victorian bun penny.
Coins that are not round (British 50 pence for example) usually have an odd number of sides, with the edges rounded off. This is so that the coin has a constant diameter, and will therefore be recognised by vending machines whichever way it is inserted. If a coin had an even number of sides this would not be possible. Some such older designs remain, however, such as the 12-sided Australian 50 cent coin.
Coins are popularly used as a sort of two-sided die; in order to choose between two options with a random possibility, one choice will be labeled "heads" and the other "tails," and a coin will be flipped or "tossed" to see whether the heads or tails side comes up on top. See Bernoulli trial; a fair coin is defined to have the probability of heads (in the parlance of Bernoulli trials, a "success") of exactly 0.5. A widely publicized example of an asymmetrical coin is the Belgian one euro coin [3]. See also coin flipping.
Coins are sometimes falsified to make one side weigh more. Such a coin is said to be "weighted."
Some coins, called bracteates, are so thin they can only be struck on one side.
Bi-metallic coins are sometimes used for higher values and for commemorative purposes. In the 1990s, France used a tri-metallic coin. Common circulating examples include the €1, €2, British £2 and Canadian $2.
Guitar-shaped coins were once issued in Somalia, Poland once issued a fan-shaped 10 złoty coin, but perhaps the oddest coin ever was the 2002 $10 coin from Nauru, a Europe-shaped coin.[4]
The Royal Canadian Mint is now able to produce holographic-effect gold and silver coinage.
For a list of many pure metallic elements and their alloys which have used in actual circulation coins and for trial experiments, see coinage metals. [5]