垄断（英语：Monopoly），或称卖者垄断、独卖、独占，一般指唯一的卖者在一个或多个市场，通过一个或多个阶段，面对竞争性的消费者；与买方垄断相反。独占者在市场上，能够随意调节价格与产量（不能同时调节）。垄断能够借由在法律上独享的特权、对供应来源的控制、或是企业间的联手或协力行为来达成。

中国自古称垄断为“榷”。古代中国的盐、铁、茶长期属于官营之垄断事业，因有暴利之故，国家一旦出现了财政危机，为贴补国用不足，必然实行禁榷制度。

一般认为，垄断的基本原因是进入障碍，也就是说，独占厂商能在其市场上保持唯一卖者的地位，是因为其它企业不能进入市场并与之竞争。产生垄断的原因有三个：

A monopoly (from Greek μόνος mónos ("alone" or "single") and πωλεῖν pōleîn ("to sell")) exists when a specific person or enterprise is the only supplier of a particular commodity (this contrasts with a monopsony which relates to a single entity's control of a market to purchase a good or service, and with oligopoly which consists of a few entities dominating an industry). Monopolies are thus characterized by a lack of economic competition to produce the good or service, a lack of viable substitute goods, and the possibility of a high monopoly price well above the firm's marginal cost that leads to a high monopoly profit. The verb monopolise or monopolize refers to the process by which a company gains the ability to raise prices or exclude competitors. In economics, a monopoly is a single seller. In law, a monopoly is a business entity that has significant market power, that is, the power to charge overly high prices. Although monopolies may be big businesses, size is not a characteristic of a monopoly. A small business may still have the power to raise prices in a small industry (or market).