U.S. insider trading prohibitions are based on English and American common law prohibitions against fraud. In 1909, well before the Securities Exchange Act was passed, the United States Supreme Court ruled that a corporate director who bought that company’s stock when he knew is was about to jump up in price committed fraud by buying while not disclosing his inside information.

Section 17 of the Securities Act of 1933 contained prohibitions of fraud in the sale of securities which were greatly strengthened by the Securities Exchange Act of 1934.

Section 16(b) of the Securities Exchange Act of 1934 prohibits short-swing profits (from any purchases and sales within any six month period) made by corporate directors, officers, or stockholders owning more than 10% of a firm’s shares. Under Section 10(b) of the 1934 Act, SEC Rule 10b-5, prohibits fraud related to securities trading.

The Insider Trading Sanctions Act of 1984 provides for penalties for illegal insider trading to be as high as three times the profit gained or the loss avoided from the illegal trading.

Insider trading, or similar practices, are also regulated by the SEC under its rules on takeovers and tender offers under the Williams Act.

Much of the development of insider trading law has resulted from court decisions. In SEC v. Texas Gulf Sulphur Co. (1966), a federal circuit court stated that anyone in possession of inside information must either disclose the information or refrain from trading.

In 1984, the Supreme Court of the United States ruled in the case of Dirks v. SEC that tippees (receivers of second-hand information) are liable if they had reason to believe that the tipper had breached a fiduciary duty in disclosing confidential information and the tipper received any personal benefit from the disclosure. (Since Dirks disclosed the information in order to expose a fraud, rather than for personal gain, nobody was liable for insider trading violations in his case.)

The Dirks case also defined the concept of "constructive insiders," who are lawyers, investment bankers and others who receive confidential information from a corporation while providing services to the corporation. Constructive insiders are also liable for insider trading violations if the corporation expects the information to remain confidential, since they acquire the fiduciary duties of the true insider.

In United States v. Carpenter (1986) the U.S. Supreme Court cited an earlier ruling while unanimously upholding mail and wire fraud convictions for a defendant who received his information from a journalist rather than from the company itself.

"It is well established, as a general proposition, that a person who acquires special knowledge or information by virtue of a confidential or fiduciary relationship with another is not free to exploit that knowledge or information for his own personal benefit but must account to his principle for any profits derived therefrom."

However, in upholding the securities fraud (insider trading) convictions, the justices were evenly split.

1n 1997 the Supreme Court adopted the misappropriation theory of insider trading in United States v. O'Hagan. O'Hagan was a partner in a law firm representing Grand Met, while it was considering a tender offer for Pillsbury Co. O'Hagan used this inside information by buying call options on Pillsbury stock, resulting in profits of over $4 million. O'Hagan claimed that neither he nor his firm owed a fiduciary duty to Pillsbury, so that he did not commit fraud by purchasing Pillsbury options.

The Court rejected O'Hagan's arguments and upheld his conviction.

The "misappropriation theory" holds that a person commits fraud "in connection with" a securities transaction, and thereby violates 10(b) and Rule 10b-5, when he misappropriates confidential information for securities trading purposes, in breach of a duty owed to the source of the information. Under this theory, a fiduciary's undisclosed, self-serving use of a principal's information to purchase or sell securities, in breach of a duty of loyalty and confidentiality, defrauds the principal of the exclusive use of the information. In lieu of premising liability on a fiduciary relationship between company insider and purchaser or seller of the company's stock, the misappropriation theory premises liability on a fiduciary-turned-trader's deception of those who entrusted him with access to confidential information.

The Court specifically recognized that a corporation’s information is its property: "A company's confidential information...qualifies as property to which the company has a right of exclusive use. The undisclosed misappropriation of such information in violation of a fiduciary duty...constitutes fraud akin to embezzlement – the fraudulent appropriation to one's own use of the money or goods entrusted to one's care by another."