A black market, underground economy or shadow economy, is a clandestine market or series of transactions that has some aspect of illegality or is characterized by some form of noncompliant behavior with an institutional set of rules. If the rule defines the set of goods and services whose production and distribution is prohibited by law, non-compliance with the rule constitutes a black market trade since the transaction itself is illegal. Parties engaging in the production or distribution of prohibited goods and services are members of the illegal economy. Examples include the drug trade, prostitution (where prohibited), illegal currency transactions and human trafficking. Violations of the tax code involving income tax evasion constitute membership in the unreported economy.^[1][2]

Because tax evasion or participation in a black market activity is illegal, participants will attempt to hide their behavior from the government or regulatory authority.^[3] Cash usage is the preferred medium of exchange in illegal transactions since cash usage does not leave a footprint.^[4] Common motives for operating in black markets are to trade contraband, avoid taxes and regulations, or skirt price controls or rationing. Typically the totality of such activity is referred to with the definite article as a complement to the official economies, by market for such goods and services, e.g. "the black market in bush meat".

The black market is distinct from the grey market, in which commodities are distributed through channels that, while legal, are unofficial, unauthorized, or unintended by the original manufacturer, and the white market, in which trade is legal and official.

Black money is the proceeds of an illegal transaction, on which income and other taxes have not been paid, and which can only be legitimised by some form of money laundering. Because of the clandestine nature of the black economy it is not possible to determine its size and scope.^[5]

The literature on the black market has not established a common terminology and has instead offered many synonyms including: subterranean; hidden; grey; shadow; informal; clandestine; illegal; unobserved; unreported; unrecorded; second; parallel and black.^[3]

There is no single underground economy; there are many. These underground economies are omnipresent, existing in market oriented as well as in centrally planned nations, be they developed or developing. Those engaged in underground activities circumvent, escape or are excluded from the institutional system of rules, rights, regulations and enforcement penalties that govern formal agents engaged in production and exchange. Different types of underground activities are distinguished according to the particular institutional rules that they violate. Four major underground economies can be identified:^[3][6]

The "illegal economy" consists of the income produced by those economic activities pursued in violation of legal statutes defining the scope of legitimate forms of commerce. Illegal economy participants engage in the production and distribution of prohibited goods and services, such as drug trafficking, arms trafficking, and prostitution.^[6]

The "unreported economy" consists of those economic activities that circumvent or evade the institutionally established fiscal rules as codified in the tax code. A summary measure of the unreported economy is the amount of income that should be reported to the tax authority but is not so reported. A complementary measure of the unreported economy is the "tax gap", namely the difference between the amount of tax revenues due the fiscal authority and the amount of tax revenue actually collected. In the U.S. unreported income is estimated to be $2 trillion resulting in a "tax gap" of $450–$600 billion.^[7][8]

The "unrecorded economy" consists of those economic activities that circumvent the institutional rules that define the reporting requirements of government statistical agencies.^[6] A summary measure of the unrecorded economy is the amount of unrecorded income, namely the amount of income that should (under existing rules and conventions) be recorded in national accounting systems (e.g. National Income and Product Accounts) but is not. Unrecorded income is a particular problem in transition countries that switched from a socialist accounting system to UN standard national accounting. New methods have been proposed for estimating the size of the unrecorded (non-observed) economy.^[9] But there is still little consensus concerning the size of the unreported economies of transition countries.^[10]

The "informal economy" comprises those economic activities that circumvent the costs and are excluded from the benefits and rights incorporated in the laws and administrative rules covering property relationships, commercial licensing, labor contracts, torts, financial credit and social security systems.^[6] A summary measure of the informal economy is the income generated by economic agents that operate informally.^[11][12] The informal sector is defined as the part of an economy that is not taxed, monitored by any form of government, or included in any gross national product (GNP), unlike the formal economy. In developed countries the informal sector is characterized by unreported employment. This is hidden from the state for tax, social security or labour law purposes but is legal in all other aspects.^[13] On the other hand, the term black market can be used in reference to a specific part of the economy in which contraband is traded.

Goods and services acquired illegally and/or transacted for in an illegal manner may exchange above or below the price of legal market transactions:

Even when the underground market offers lower prices, consumers still have an incentive to buy on the legal market when possible, because:

However, in some limited situations, consumers conclude that they are actually better off using black market services, particularly when government regulations hinder what would otherwise be a legitimate competitive service. For example:

Some examples of underground economic activities include:

Prostitution is illegal or highly regulated in many countries across the world. These places form a classic study of the underground economy, because of consistent high demand from customers, relatively high pay, but labor-intensive and low skilled work, which attracts a continual supply of workers. While prostitution exists in every country, studies show that it tends to flourish more in poorer countries, and in areas with large numbers of unattached men, such as around military bases.^[17] For instance, an empirical study showed that the supply of prostitutes rose abruptly in Denver and Minneapolis in 2008 when the Democratic and Republican National Conventions took place there.^[18]

Prostitutes in the black market generally operate with some degree of secrecy, sometimes negotiating prices and activities through codewords and subtle gestures. In countries such as Germany or the Netherlands, where prostitution is legal but regulated, illegal prostitutes exist whose services are offered cheaper without regard for the legal requirements or procedures—health checks, standards of accommodation, and so on.

In other countries, such as Nicaragua, where legal prostitution is regulated, hotels may require both parties to identify themselves, to prevent the rise of child prostitution.

Personally identifying information, financial information like credit card and bank account information, and medical data is bought and sold, mostly in darknet markets.^[19] People increase the value of the stolen data by aggregating it with publicly available data, and sell it again for a profit, increasing the damage that can be done to the people whose data was stolen.^[20]

From the late 19th and early 20th centuries, many countries began to ban the keeping or using of some recreational drugs, such as the United States' war on drugs. Many people nonetheless continue to use illegal drugs, and a black market exists to supply them. Despite law enforcement efforts to intercept them, demand remains high, providing a large profit motive for organized criminal groups to keep drugs supplied. The United Nations has reported that the retail market value of illegal drugs is $321.6 billion USD.^[21]

Although law enforcement agencies intercept a fraction of the illegal drugs, and incarcerate hundreds of thousands of wholesale and retail sellers, the very stable demand for such drugs and the high profit margins encourages new distributors to enter the market without a decrease in the retail price. Many drug legalization activists draw parallels between the illegal drug trade and the Prohibition of alcohol in the United States in the 1920s.

The legislatures of many countries forbid or restrict the personal ownership of weapons. These restrictions can range from small knives to firearms, either altogether or by classification (e.g. caliber, handguns, automatic weapons, and explosives). The black market supplies the demands for weaponry that can not be obtained legally, or may only be obtained legally after obtaining permits and paying fees. This may be by smuggling the arms from countries where they were bought legally or stolen, or by stealing from arms manufacturers within the country itself, using insiders. In cases where the underground economy is unable to smuggle firearms, they can also satisfy requests by gunsmithing their own firearms. Those who may buy this way include criminals to use for illegal activities, gun collectors, and otherwise law-abiding citizens interested in protecting their dwellings, families or businesses.

In England and Wales, certain categories of weapons used for hunting may be owned by qualified residents but must be registered with the local police force and kept within a locked cabinet. Another segment of the population who may purchase weapons on the black market are individuals who are unable to pass the legal requirements for registration—convicted felons or those suffering from mental illness for example. In a few jurisdictions, collectors may legally keep antique weapons made incapable of being readily restored to a firing condition.

The illegal logging of timber has posed as an issue. According to Interpol, the illegal logging industry is worth almost as much as drug production industry, in some countries.^[22][23]

In many developing countries, living animals are captured in the wild and sold as pets. Wild animals are also hunted and killed for their meat, hide, and organs, the latter of which and other animal parts are sold for use in traditional medicine.

In several of the states within the United States, laws requiring the pasteurization of milk has created black market situations involving the transport and sale of raw milk, and sometimes raw milk cheese which is legal in a number of EU countries but banned in the US if aged less than 60 days^[24]

Rum-running, or bootlegging, is the illegal business of transporting (smuggling) alcoholic beverages where such transportation is forbidden by law. Smuggling is usually done to circumvent taxation or prohibition laws within a particular jurisdiction. The term rum-running is more commonly applied to smuggling over water; bootlegging is applied to smuggling over land. According to the PBS documentary Prohibition, the term "bootlegging" was popularized when thousands of city dwellers would sell liquor from flasks they kept in their boot leg all across major cities and rural areas.^[25][26] The term "rum-running" most likely originated at the start of Prohibition in the United States (1920–1933), when ships from Bimini in the western Bahamas transported cheap Caribbean rum to Florida speakeasies. But rum's cheapness made it a low-profit item for the rum-runners, and they soon moved on to smuggling Canadian whisky, French champagne, and English gin to major cities like New York City and Boston, where prices ran high. It was said that some ships carried $200,000 in contraband in a single run.

It has been reported that smuggling one truckload of cigarettes from a low-tax US state to a high-tax state can lead to a profit of up to $2 million.^[27] The low-tax states are generally the major tobacco producers, and have come under enormous criticism for their reluctance to increase taxes. North Carolina eventually agreed to raise its taxes from 5 cents to 35 cents per pack of 20 cigarettes, although this remains far below the national average.^[28] But South Carolina has so far refused to follow suit and raise taxes from seven cents per pack (the lowest in the USA).^[29]

In the UK, it has been reported that "27% of cigarettes and 68% of roll your own tobacco is purchased on the black market".^[30]

According to the World Health Organization (WHO), illegal organ trade occurs when organs are removed from the body for the purpose of commercial transactions.^[31] The WHO justifies its stance on the issue by stating, "Payment for ... organs is likely to take unfair advantage of the poorest and most vulnerable groups, undermines altruistic donation and leads to profiteering and human trafficking."^[32] Despite these ordinances, it was estimated that 5% of all organ recipients engaged in commercial organ transplant in 2005.^[33] Research indicates that illegal organ trade is on the rise, with a recent report by Global Financial Integrity estimating that the illegal organ trade generates profits between $600 million and $1.2 billion per year with a span over many countries.

A racket is a service that is fraudulently offered to solve a problem, such as for a problem that does not actually exist, that will not be put into effect, or that would not otherwise exist if the racket did not exist. Conducting a racket is racketeering.^[34] Particularly, the potential problem may be caused by the same party that offers to solve it, although that fact may be concealed, with the specific intent to engender continual patronage for this party. An archetype is the protection racket, wherein a person or group (e.g., a criminal gang) indicates to a store owner that they could protect her/his store from potential damage, damage that the same person or group would otherwise inflict, while the correlation of threat and protection may be more or less deniably veiled, distinguishing it from the more direct act of extortion. Racketeering is often associated with organized crime, and the term was coined by the Employers' Association of Chicago in June 1927 in a statement about the influence of organized crime in the Teamsters union.^[35]

Where taxicabs, buses, and other transportation providers are strictly regulated or monopolized by government, a black market typically flourishes to provide transportation to poorly served or overpriced communities. In the United States, some cities restrict entry to the taxicab market with a medallion system, i.e., taxicabs must get a special license and display it on a medallion in the vehicle. In most such jurisdictions it is legal to sell the medallions, but the limited supply and resulting high prices of medallions have led to a market in unlicensed carpooling/illegal taxicab operation. In Baltimore, Maryland, for example, it is not uncommon for private individuals to provide illegal taxicab service^[16] for city residents.

In places where there is rent control there may be a black market for housing. For instance, in the UK there is illegal subletting of social housing homes where the tenant illegally rents out the home at a higher rent.^[36] In Sweden, rental contracts with regulated rent can be bought on the black market,^[37] either from the current tenant or sometimes directly from the property owner. Specialised black-market dealers assist the property owners with such transactions.^[38] In India, places like Chennai, Bangalore, Hyderabad, Mumbai, Kolkotta and New Delhi, where students are coming from all over India, getting high rented paying guests or other forms of rented apartments without any taxation or regulations.

Medicines and essential aircraft and automobile parts (e.g. brakes, motor parts, etc.) are counterfeited on a large scale.

Street vendors in countries where there is little enforcement of copyright law, particularly in Asia and Latin America, often sell deeply discounted copies of films, music CDs, and computer software such as video games, sometimes even before the official release of the title. A determined counterfeiter with a few hundred dollars can make copies that are digitally identical to an original and face no loss in quality; innovations in consumer DVD and CD writers and the widespread availability of cracks on the Internet for most forms of copy protection technology make this cheap and easy to do.

Copyright-holders and other proponents of copyright laws have found this phenomenon hard to stop through the courts, as the operations are distributed and widespread, transversing national borders and thus legal systems. Since digital information can be duplicated repeatedly with no loss of quality, and passed on electronically at little to no cost, the effective underground market value of media is zero, differentiating it from nearly all other forms of underground economic activity. The issue is compounded by widespread indifference to enforcing copyright law, both with governments and the public at large. To steal a car is seen as a crime in most people's eyes, but to obtain unauthorized copies of music or a game is not.^[39] Additionally, not all people agree with 'copyright laws', as it unfairly criminalises competition, allowing the copyright-holder to effectively monopolise related industries. It also authorises copyright-holders to use region-coding to discriminate against selected populations price-wise and availability-wise.

The comparison to car-theft, although common, is not truly analogous. Automobile theft results in an item being removed from the owner with the ownership transferred to a second party. Media piracy is a crime of duplication, with no physical property being stolen. Copyright infringement law goes as far as to deem illegal "mixtapes" and other such material copied to tape or disk. Copyright holders typically attest the act of theft to be in the profits forgone to the pirates. However, this makes the unsubstantiated assumption that the pirates would have bought the copyrighted material if it had not been available through file sharing or other means. Copyright holders also say that they did some work for creating their copyrighted material and they wish to get compensated for their work. No other system than copyright has been found to compensate the artists and other creators for their work, and many artists do not have any alternative source of income or another job. Many artists and film producers have accepted the role of piracy in media distribution.^[40] The spread of material through file sharing is a major source of publicity for artists and has been shown to build fan bases that may be more inclined to see the performer live^[41] (live performances make up the bulk of successful artists' revenues,^[42] however not all artists can make live performances, for example photographers typically only have a single source of income that is the licensing of their photos).

Money itself is traded on the black market. This may happen for one or more of several reasons:

A government may officially set the rate of exchange of its currency with that of other currencies, typically the US dollar. When it does, the peg often overvalues the local currency relative to what its market value would be if it were a floating currency. Those in possession of the "harder" currency, for example expatriate workers, may be able to use the black market to buy the local currency at better exchange rates than they can get officially.

In situations of financial instability and inflation, citizens may substitute a foreign currency for the local currency. The U.S. dollar is viewed as a relatively stable and safe currency and is often used abroad as a second currency. In 2012, $340 billion, roughly 37 percent^[44] of all U.S. currency, was believed to be circulating abroad.^[45] The most recent study of the amount of currency held overseas suggests that only 25 percent of U.S. currency is presently held abroad.^[46] The widespread substitution of U.S. currency for local currency is known as de facto dollarisation, and has been observed in transition countries such as Cambodia^[47] and in some Latin American countries.^[48] Some countries, such as Ecuador, abandoned their local currency and now use US dollars, essentially for this reason, a process known as de jure dollarization. See also the example of the Ghanaian cedi from the 1970s and 1980s.

If foreign currency is difficult or illegal for local citizens to acquire, they will pay a premium to acquire it. U.S. currency is viewed as a relatively stable store of value and since it does not leave a paper trail, it is also a convenient medium of exchange for both illegal transactions and for unreported income both in the U.S and abroad.^[49]

More recently cryptocurrencies such as bitcoin have been used as medium of exchange in black market transactions. Cryptocurrencies are sometimes favored over centralized currency due to their anonymous nature and their ability to be traded over the internet.^[50]

In the EU, it is not illegal for a person or business to buy fuel in one EU state for their own use in another, but as with other goods the tax will generally be payable by the final customer at the physical place of making the purchase.

Between the Republic of Ireland and Northern Ireland, there has often been a black market in petrol and diesel.^[51][52] The direction of smuggling can change depending on the variation of the taxes and the exchange rate between the Euro and Pound Sterling; indeed sometimes diesel will be smuggled in one direction and petrol the other.

In some countries, diesel fuel for agricultural vehicles or domestic use is taxed at a much lower rate than that for other vehicles. This is known as dyed fuel, because a coloured dye is added so it can be detected if used in other vehicles (e.g. a red dye in the UK, a green dye in Ireland). Nevertheless, the saving is attractive enough to make a black market in agricultural diesel. In 2007 it was estimated that £350 million was not gained in profit as a result of this phenomenon, in the UK.^[53]

In countries like India and Nepal, the price of fuel is set by the government, and it is illegal to sell the fuel over the set price. Due to the petrol crisis in Nepal, black marketing in fuel has been a common trend, especially during mass petrol shortage. At times, people need to queue for hours or even sometimes overnight to get the fuel. On the other hand, the petrol pump operators are alleged to hoarding the fuel, and selling it to black marketers. Black marketing in vehicle/cooking fuel became widespread during the 2015 economic blockade imposed on Nepal. Even after the economic blockade was eased, and petrol imports resumed, people are not getting the fuel as they were supposed to and are resort to buying from the black market.

There are some countries where sex toys are illegal, such as Saudi Arabia, Thailand and India. The illegality has omitted certain clearing processes such as safety testing when they are sold by undercover independent vendors on the black market. Other black market platforms used to sell sex toys on the black market include consumer-to-consumer online auction websites, as well as private pages on social media websites.^[54] In black market venues in Cambodia, sex toys have been seized alongside aphrodisiac products.^[55] Some analysts have argued that if efforts in North America to ban realistic-looking sexbots succeed, it may result in a black market trade in sexbots.^[56]

People engaged in the black market usually run their business hidden under a front business that is legal.

Often, certain types of illegal products are traded against one another, depending on the geographical location.^[57]

Black markets flourish in most countries during wartime. States that are engaged in total war or other large-scale, extended wars often impose restrictions on home use of critical resources that are needed for the war effort, such as food, gasoline, rubber, metal, etc., typically through rationing. In most cases, a black market develops to supply rationed goods at exorbitant prices. The rationing and price controls enforced in many countries during World War II encouraged widespread black market activity.^[58] One source of black-market meat under wartime rationing was by farmers declaring fewer domestic animal births to the Ministry of Food than actually happened. Another in Britain was supplies from the US, intended only for use in US army bases on British land, but leaked into the local native British black market.

For example, in the Parliament of the United Kingdom on February 17, 1945,^[59] members said that "the whole turkey production of East Anglia had gone to the black market" and "prosecutions [for black-marketing] were like trying to stop a leak in a battleship", and it was said that official prices of such foods were set so low that their producers often sold their produce on the black market for higher prices; one such route (seen to operate at the market at Diss in Norfolk) was to sell live poultry to members of the public, and each purchaser would sign a form promising that he was buying the birds to breed from, and then take them home for eating.

During the Vietnam war, American soldiers would spend Military Payment Certificates on maid service and sexual entertainment,. Also if a Vietnamese civilian wanted something that was hard to get, he would buy it at double the price from one of the soldiers, who had a monthly ration card and thus had access to the military stores. The transactions ran through the on-base maids to the local populace. Although these activities were illegal, only flagrant or large-scale black-marketeers were prosecuted by the military.

A classic example of new regulation creating a black market is the prohibition of alcohol. Similarly, when the law disappears, so does the black market, which is why of the arguments for marijuana legalization is the elimination of the black market and thus taxes from that economy being used by the government.

In India, "black money" refers to funds earned on the black market, on which income and other taxes have not been paid. The black money market situation in India is epidemic. India currently tops the list for illegal monies in the entire world, estimated to be almost US$1,456 billion stored in Swiss banks in the form of unaccounted money.^[60] According to the data provided by the Swiss Banking Association, India has more black money than the rest of the world combined.^[61][62][63] Indian Swiss bank account assets are worth 13 times (1300%) the country’s national debt, and, if this black money is seized and brought back to the country, India has the potential to become one of the richest countries in the world.^[64] Allegations of Indians holding trillions in black money in Switzerland are, however, in dispute. Later reports, including those by Swiss Bankers Association and the Government of Switzerland, claim that these allegations are false and fabricated, and the total amount held in all Swiss banks by citizens of India is about US$2 billion.^[65][66]