Not all intellectual property rights grant the right to exclude that is indicative of “property rules,” as that term was used by Guido Calabresi and A. Douglas Melamed in their seminal article. Some intellectual property rights are “liability rules,” in which the right holder has an entitlement to compensation for use of the protected invention, not a right to preclude the use. Although patent laws normally grant a right to exclude others from use of the protected invention as a default, most countries’ laws allow the government to convert the patent property rule into a liability rule through a compulsory license. It has been noted, for example, that by the end of the 1950s, the U.S. had issued compulsory licenses covering 40 to 50 thousand patents, including substantial portions of the patent portfolios of AT&T, General Electric, IBM, and Xerox. The U.S. Supreme Court recently expressed a willingness to accept liability rules over injunctions in some patent infringement cases.