Prior to the mid-nineteenth century, American legislatures and courts conceived of the patent as an active tool of economic growth. Patents were issued to both inventors and “promoters” who promised to deploy technology that had already been invented. In the 1830s a much more classical conception of the patent emerged, as a property right pure and simple. Questions about whether and how to employ patents were lodged almost entirely with their owners, who even acquired the power to keep patented technology off the market, precisely contrary to what the original Framers had in mind. An essential part of this development was the rise of federal patent exclusivity—a result that was not mandated by the text of the Constitution’s IP Clause. Only federal exclusivity could limit the power of the states to grant unwarranted exclusive rights to favored grantees. The result was a regime in which Congress acquired the exclusive power to award patents for inventions, while state law largely controlled post-issuance commerce in patents. Changes in U.S. patent law under the 1836 Patent Act and later were driven by the classical belief that monopoly undermines economic growth, with invention as a narrow exception. This entailed two requirements: (1) the conditions for obtaining a patent be narrow, limited to actual inventions within the applicant’s possession, and adequately disclosed; and (2) patent issuance had to be made a nonpolitical, administrative action. Together these requirements led both Congress and the courts away from relatively open ended policy concerns, and toward technical specification and boundary clarity. The result was a patent system increasingly detached from questions about economic development.