Currency, a monetary unit of a country (e. g., the Soviet rouble, British pound sterling, Bulgarian lev); a type of monetary system (gold, silver, banknote); the aggregate amount of money used by a country in its international settlements (foreign currency). The world has had two prevailing types of monetary system: monometallism, when one metal was used, and bimetallism, when both gold and silver were equally involved in circulation. Since the latter half of the 19th century, gold has prevailed as a monometal in most European countries. The epoch of the general crisis of capitalism is as a whole characterised by a monetary system based on banknotes; they are only symbols of gold, which continues to play the role of universal equivalent, and replace gold only as a medium of circulation and a means of payment. This system creates the basis for chronic inflation, periodical devaluation and permanent monetary crisis. Capitalist currencies are subdivided into convertible, which can be exchanged for any foreign currency (e. g., the US dollar), partially convertible, which can be exchanged only in certain monetary transactions and even then not by all owners (the currencies of most West European countries), and inconvertible (closed), which are only circulated within the boundaries of a single country. The US dollar plays the principal role in the capitalist monetary system: it is a key (reserve) currency of the capitalist world. Most international settlements are effected and world market prices fixed in dollars. The pound sterling is also widely used. Recently, the West German mark, the Japanese yen and the French franc have acquired greater weight in international settlements. Typical of the capitalist monetary system today is the dollar crisis; it is a major manifestation of the crisis which has plagued the imperialist financial and monetary system and which directly hinges on US military and economic expansion and steadily mounting inflation. The currency of the socialist countries is, on the contrary, characterised by a stable nature rooted in the advantages of the socialist economic system, which is based on social ownership of the means of production, the balanced development of the socialist economy, and planned money circulation and commodity turnover. The stability of socialist currencies is guaranteed by the mass of commodities brought into circulation at planned prices, which have been set and maintained on a stable level. A certain role is played by the gold reserves at the disposal of the socialist countries, which they draw on to regulate their balance of payments with the capitalist countries and to buy the commodities they need to augment their commodity supplies. Of crucial importance in ensuring the stability of currency, however, is the planning of foreign economic ties and the state’s monopoly of foreign currency; they enable the state to concentrate it in its hands and withdraw it from internal circulation, which shields the socialist countries’ monetary circulation and domestic market against the spontaneous vacillations typical of the capitalist monetary market.