内线交易，亦作内幕交易，是指：于获悉未公开且后来证实足以影响股票或其他有价证券市价的消息后，进行交易，并有成比例的获利发生的行为。 即内线交易的要件在于：

内线交易可以是完全合法的证券交易行为，但是由于内线交易造成市场不公平，所以在多数情况之下，内线交易常被使用在违法的犯罪行为描述。 虽然有经济学家肯定内线交易对于资本市场的效率和流动性都有正面帮助，但是世界各国多半都把内线交易列为违法行为。

Insider trading is the trading of a public company's stock or other securities (such as bonds or stock options) by individuals with access to nonpublic information about the company. In various countries, some kinds of trading based on insider information is illegal. This is because it is seen as unfair to other investors who do not have access to the information, as the investor with insider information could potentially make far larger profits that a typical investor could not make.