The Intellectual Property Clause (“IP Clause”) of the US Constitution has long been a puzzle for courts and commentators. It authorizes Congress to secure exclusive property rights for authors and inventors, but it does not use the terms “patent” or “copyright,” and its objects of “Science” and “useful Arts” do not cleanly map onto the subject matter of current patent and copyright systems. As the Supreme Court has noted, under popular usage of the terms “arts” and “science,” one would expect patents to promote science and copyrights to promote arts, yet we know from the historical record that exactly the opposite is the case. Other terms, such as “progress” and “discoveries,” remain contested. IP Clause interpretations to date rely exclusively on British legal and intellectual antecedents. I argue that the great French Encyclopédie project—a landmark of the mid-eighteenth-century Enlightenment—provides crucial context to the IP Clause. James Madison, a drafter of the IP Clause, owned and approvingly cited the work. Founding Fathers Thomas Jefferson and Benjamin Franklin were enthusiastic advocates of the Encyclopédie. The Encyclopédie has as its twin goals the promotion of progress in science and in mechanical (useful) arts. I argue that the reliance of early courts and commentators on British antecedents to interpret the federal patent and copyright statutes led to an improperly narrow sense of the context of the IP Clause. Using entries from the Encyclopédie on “art,” “science,” “discoveries,” “inventions,” “writers/authors,” and other relevant topics, I propose a new interpretation of the IP Clause that is more coherent and compelling than existing accounts.