A market in which certain goods or services are routinely traded in a manner contrary to the laws or regulations of the government in power. Typical reasons why the market goes underground in this way include the desire by substantial numbers of buyers and sellers to evade restrictive government price controls or inconvenient rationing schemes, to avoid paying heavy taxes on the good or service in question, or simply to be able to obtain forbidden goods or services that the government does not want the people to have at all. The size and relative importance of black markets vary greatly from one country to another and from one historical period to the next within any single country.