Currency is a standardized form of money that we use every day to buy and sell things, and its value can change based on many factors.

Key idea: Early currency evolved from receipts for stored goods to various commodities and eventually to metal objects, reflecting the need for a reliable way to trade.

The idea of currency started a very long time ago. In ancient Mesopotamia and Egypt, people used receipts for grain stored in temples as an early form of currency. Metals then became symbols for this stored value. This system worked for over 1500 years in the Fertile Crescent.

However, this early system had a weakness: if there was no safe place to store goods, the value of the 'money' depended on how well those goods were protected. Trade could only happen as far as the military's ability to keep things safe. Later, during the late Bronze Age, treaties helped make trade routes safer around the Eastern Mediterranean. It is thought that copper shaped like oxhides, made in Cyprus, might have been used as currency during this time.

When piracy increased during the Bronze Age collapse, this trading system likely ended. Prosperity returned with Phoenician trade around the 10th and 9th centuries BC, leading to the first real coins, possibly in Anatolia. In Africa, many different things were used as money, like beads, ivory, livestock, and shell money. For example, 'manilla' rings were used in West Africa from the 15th century to buy and sell enslaved people. Even today, African currencies are very diverse, and in some places, people still trade goods directly without using money, which is called barter.

Key idea: Metal coins became a standardized form of currency, with their value often tied to the precious metal they contained, leading to more reliable trade and the development of banking.

When metal coins became common, the metal itself often became the source of value. At first, copper was used, then silver and gold, and sometimes bronze. Today, coins are often made from less valuable metals. Metals were mined, weighed, and then stamped to create coins. This stamping was a guarantee that the person receiving the coin was getting a specific, known weight of precious metal.

Even though coins could be faked, having standard coins led to a new way of counting value, which helped banking develop. A discovery by Archimedes made it easy to check the true metal content of a coin, even if it had been altered. This helped people trust the value of coins.

Most major economies that used coins had different levels of coins with different values: gold for large purchases, silver for medium transactions, and copper or mixed metals for everyday spending. Gold was always the most valuable because it was rare, followed by silver, and then copper. The exact value differences changed over time and in different places, for example, when new silver mines were discovered.

“The stamping on coins was a guarantee that the person receiving the coin was getting a specific, known weight of precious metal.”

Key idea: Paper money emerged as a practical alternative to heavy coins, offering convenience but also introducing challenges like inflation and the need for trust in government backing.

In ancient China, carrying many heavy copper coins became difficult, especially for large transactions or loans. This led to the invention of paper money, also known as banknotes. This change happened gradually from the late Tang dynasty into the Song dynasty. It started with merchants exchanging heavy coins for receipts from wholesalers, which could be used temporarily in a small area.

By the 10th century, the Song government began using these notes among traders in its salt industry. Eventually, the government took over the shops that issued these notes, creating state issued paper currency. However, these early banknotes were still only valid locally and for a short time. It was not until the mid 13th century that a standard, nationwide paper money became widely accepted. The existing methods of woodblock printing and later movable type printing helped mass produce this paper money.

Around the same time, from the 7th to 12th centuries, the Islamic world developed a strong money based economy using a stable, high value currency called the dinar. Muslim economists and traders introduced many new financial ideas, such as credit, checks, promissory notes, savings accounts, and banking institutions.

In Europe, paper currency was regularly introduced in Sweden in 1661. Sweden had a lot of copper, so its copper coins were very large and heavy. Paper currency offered several benefits: it reduced the need to transport risky gold and silver, made it easier to lend gold or silver at interest, and allowed for different types of currency, some backed by credit and some by precious metals. It also helped with investing in companies.

However, paper money also had drawbacks. Since paper itself has no value, governments could print more notes than they had precious metals to back them. This increased the amount of money in circulation, which could lead to inflation, meaning money buys less. David Hume noted this in the 18th century. This could create an 'inflationary bubble' that might burst if people lost faith in paper money and demanded physical gold or silver. Printing paper money was also linked to financing wars, which made some people suspicious of it. Despite these concerns, the potential for large profits from trade and investment made paper money appealing.

By 1900, most industrial nations used some form of the gold standard, where paper money and silver coins were used daily, but their value was tied to gold. Many countries, especially during wars or financial crises, eventually moved away from the gold standard. The United States officially left the gold standard in 1971, an event known as the Nixon shock. Today, no country uses a gold or silver standard for its currency.

“Paper currency had several advantages: it reduced the need to transport gold and silver, which was risky.”

Key idea: Banknotes are a common form of currency, evolving from paper to more durable and secure polymer materials.

A banknote is a type of paper currency, often used as legal tender. Along with coins, banknotes make up the physical cash we use. While banknotes were traditionally made of paper, Australia developed polymer currency in the 1980s. These plastic notes last longer and are harder to counterfeit. By 2016, over 20 countries were using polymer currency.

Key idea: Modern currencies are increasingly digital, and international standards like ISO 4217 help identify them globally, though symbols can vary.

Modern currency is rapidly moving into digital forms, driven by new financial technologies and less physical transactions. This includes online and mobile payments, as well as digital currencies like cryptocurrencies, stablecoins, and government backed central bank digital currencies (CBDCs).

Each country generally decides what currency it will use, a concept known as 'lex monetae'.

To help identify currencies worldwide, the International Organization for Standardization (ISO) created a system in 1978. This system, called ISO 4217, uses three letter codes to represent currencies. For example, 'USD' for United States Dollar. The first two letters usually refer to the country, and the third letter to the currency itself. Many currencies also have symbols, like '$' for the dollar or '€' for the Euro, but these symbols are not globally standardized and can be used by different currencies.

Key idea: Central banks manage currency supply and exchange rates through monetary policy, influencing economic activity and international trade.

Usually, a central bank has the sole power to issue all forms of currency, including coins and banknotes, and to control other currencies circulating in its area. It manages how much currency banks create through something called monetary policy.

When two countries trade, their currencies need to be exchanged. The price at which one currency can be swapped for another is called the exchange rate. Exchange rates can be 'floating,' meaning their value changes daily based on market supply and demand, or 'fixed,' where governments step in to keep the rate stable. If a currency's value goes up (appreciates), imports become cheaper and exports more expensive. If its value goes down (depreciates), exports become more competitive but imports cost more. These changes are influenced by things like supply and demand, interest rates, trade balances, and a country's economic strength.

The institution that controls a country's monetary policy is called the monetary authority. This is often the central bank or a Ministry of Finance. These authorities have different levels of independence from the government that created them.

Monetary policy involves controlling the amount of money available in an economy and how new money is introduced. Economic information like a country's total economic output (GDP), inflation rates, and industry growth can all affect monetary policy. For example, a central bank might change the interest rates it charges to commercial banks. These commercial banks then adjust their own rates for customers, which can encourage or discourage borrowing, spending, and business activity. This, in turn, affects economic growth and inflation.

It is interesting to note that several countries can use the same name for their currency (like the 'dollar' in Australia, Canada, and the United States). Conversely, multiple countries can use the exact same currency (like the Euro). Sometimes, one country even declares another country's currency as legal tender, meaning it is officially accepted for payments. For example, Panama and El Salvador use the US dollar. A reserve currency is a globally recognized currency held by central banks to help with international trade and stabilize exchange rates. The US dollar has been the main reserve currency since 1944, making up about 57% of global foreign exchange reserves.

Most currencies have a main unit (like the dollar or euro) and a smaller fractional unit, usually 1/100th of the main unit (like cents). Some currencies, like the Icelandic króna and Japanese yen, do not have smaller units. Mauritania and Madagascar are unique because their fractional units are not based on a decimal system, though these smaller units are rarely used today due to inflation.

Key idea: Currency convertibility describes how freely a currency can be exchanged for others, ranging from fully open to completely restricted, influenced by trade, investment, and government policies.

Currency convertibility refers to how easily a local currency can be exchanged for another currency, with or without government control. This happens in the foreign exchange market. Currencies are classified based on these restrictions:

1. Fully convertible: There are no limits on how much currency can be traded internationally, and the government does not artificially set its value. The US dollar is an example.

2. Partially convertible: Central banks control international investments. While local transactions are usually fine, there are significant restrictions on international investing, and special permission is often needed to convert to other currencies. The Indian rupee and Chinese renminbi are examples.

3. Nonconvertible: The government does not participate in the international currency market and does not allow individuals or companies to convert its currency. These are also called 'blocked' currencies, like the North Korean won.

The exchange rate between currencies is affected by the supply and demand for different currencies, which comes from three main areas:

* Trade in goods and services: When countries buy and sell goods and services from each other, it affects the demand for their currencies. For example, if many tourists visit a country, they need to exchange their money for the local currency, increasing its demand.

* Capital flows: People and companies invest across borders. If a country offers good investment opportunities, foreign money flows in, increasing demand for that country's currency. Interest rate changes and stock market fluctuations also influence these flows.

* National policies: A country's trade policies (like tariffs), monetary policies (like interest rates), and fiscal policies (like taxes and government spending) all affect its currency's value. These policies link the domestic currency to foreign currencies and influence exchange rates.

Achieving full currency convertibility is often seen as a sign of a strong economy, but it requires certain conditions: a strong microeconomy (competitive businesses), a stable macroeconomy (no high inflation), an open economy (good international trade balance), and an appropriate exchange rate system.

Key idea: Digital currencies and cryptocurrencies are emerging alternatives, but they differ from traditional currencies in their backing, regulation, and potential for misuse.

In recent years, the idea of digital currency has grown. It is still uncertain whether government backed digital money, like China's digital renminbi, will become widely used. Digital currencies not issued by governments, such as cryptocurrencies like Bitcoin, are different because their value depends entirely on the market and they do not have a safety net.

Many countries are concerned about cryptocurrencies because they can be used for illegal activities like scams, ransomware, money laundering, and terrorism. In the United States, the IRS treats virtual currency as property for tax purposes.

Besides government controlled currencies, there are also private, decentralized systems that support alternative trading tools, often called cryptocurrencies. Most of these are not backed by physical assets. The U.S. Commodity Futures Trading Commission declared Bitcoin a commodity in 2019.

Historically, there were also 'pseudo currencies' like company scrip, which were wages that could only be spent in stores owned by the employer. Modern local exchange trading systems (LETS) are more like barter than true currency. Governments often outlaw alternative currencies to protect the legitimacy of their official currency. For example, the US Constitution gives Congress the power to coin money and regulate its value, ensuring a single monetary system. Creating private currency systems to compete with the official US currency is against federal law.

Key idea: Local currencies are independent monetary systems designed for small regions, aiming to boost local economies but facing challenges related to broader economic integration and regulation.

A local currency is money that is not backed by a national government and is meant to be used only in a small area. Supporters, like Jane Jacobs, believe this can help economically struggling regions by giving people a way to exchange services and local goods. This is similar to the original purpose of all money.

However, critics argue that local currencies can create barriers that hinder large scale economies and competitive advantages. They also worry that local currencies could be used to avoid taxes. Local currencies can also appear during times of national economic trouble. For example, during Argentina's economic crisis in 2002, IOUs issued by local governments started acting like local currencies.

One well known example is the original LETS currency, started on Vancouver Island in the early 1980s. At that time, high interest rates made it hard to get regular money and credit, so people created a local currency to help trade goods and services among themselves.