Monopoly, also known as a monopoly seller, selling alone, exclusive, generally refers only to one or more sellers in the market, through one or more stages, in the face of competitive consumer; and monopsony opposite. Monopoly on the market, can freely adjust the price and yield (not simultaneously adjust). Monopoly can be legally exclusive privilege to control sources of supply, or together or work together to achieve the behavior of enterprises. 
China since ancient times called monopoly to "knock" . Ancient Chinese salt, iron, tea cause long a monopoly of the government-run, because there it is profiteering, the country once the financial crisis, to subsidize the country with a lack of implementation of the ban inevitable knock system.
Generally believed that the basic cause of monopoly is barriers to entry, that is, a monopolist can maintain sole seller of its position in the market, because the other companies can not enter the market and compete. There are three causes of monopoly:
Natural monopolies (natural monopoly): cost of production make a single producer more efficient than a large number of producers. This is the most common form of monopoly. Resources monopoly: a business owned by a key resource (such as: wireless TV dubbing industry ). Administrative monopoly: Government to give a firm the exclusive production of a product or service rights (public franchise). There are also self-monopolized by the government, known as the monopoly.
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