独占；垄断(monopoly)
一项产品或服务的供给者对市场进行排他式的占有，以致没有其他替代者。在缺乏竞争的情境下，供给者为了追求最大的利润，通常会限制产量并抬高价格。纯粹的独占概念，通常只见於理论上的讨论，在现实世界则极少发生。在某些情况下，若供给者超过一个则可能会降低效率（例如电力、瓦斯、自来水），经济学家则称之为「自然独占」（natural monopoly）（参阅public utility）。若要形成独占，就必须对竞争厂商的进入设置障碍，如果是自然独占，则是由政府来设置障碍；不论是地方政府自己经营提供服务，或是授权私人企业特许经营再加以规范。在某些情况下，设置障碍会使用较有效率的专利权；在其他情况，排除竞争对手的障碍则会采用「技术」（technical）手段。大规模、整合性的企业运作，可以增加效率、降低成本，如果因为成本降低而使得产品售价降低，则不仅厂商获利，消费者也能蒙受其惠。但很多情况下，设置障碍通常造成厂商的反竞争行为，因此大多数的自由企业经济体，都会制定法律以免企业独占造成消费者权益受损。美国的反托拉斯法（antitrust laws）是这种防止独占立法的最古老范例；公用事业法因为是附属於自然独占，是英国习惯法（common laws）的衍生产物。对於妨碍竞争的合并（mergers）或购并（acquistions），反托拉斯法都明文禁止。但这里最大的问题是，消费者会因为企业更有效率而得到好处，或是会因为企业低成本高售价而受到惩罚。亦请参阅oligopoly。
English version：
monopoly
Exclusive possession of a market by a supplier of a product or service for which there is no substitute. In the absence of competition, the supplier usually restricts output and increases price in order to maximize profits. The concept of pure monopoly is useful for theoretical discussion but is rarely encountered in actuality. In situations where having more than one supplier is inefficient (e.g., for electricity, gas, or water), economists refer to “natural monopoly” (see public utility). For monopoly to exist there must be a barrier to the entry of competing firms. In the case of natural monopolies, the government creates that barrier. Either local government provides the service itself, or it awards a franchise to a private company and regulates it. In some cases, the barrier is attributable to an effective patent. In other cases, the barrier that eliminates competing firms is technological. Large-scale, integrated operations that increase efficiency and reduce production costs confer a benefit on firms that adopt them and may confer a benefit on consumers if the lower costs lead to lower product prices. In many cases, the barrier is a result of anticompetitive behavior on the part of the firm. Most free-enterprise economies have adopted laws to protect consumers from the abuse of monopoly power. The U.S. antitrust laws are the oldest examples of this type of monopoly-control legislation; public-utility law is an outgrowth of the English common law as it pertains to natural monopolies. Antitrust law prohibits mergers and acquisitions that lessen competition. The question asked is whether consumers will benefit from increased efficiency or be penalized with a lower output and a higher price. See also oligopoly.