Against Intellectual Property
This monograph is justifiably considered a modern classic. It is by Stephan Kinsella who caused a worldwide rethinking among libertarians of the very basis of intellectual property. Mises had warned against patents, and Rothbard did too. But Kinsella goes much further to argue that the very existence of patents are contrary to a free market, and adds in here copyrights and trademarks too. They all use the state to create artificial scarcities of non-scarce goods and employ coercion in a way that is contrary to property rights and the freedom of contract.
Many people who read this essay for the first time were unprepared for the rigor of his argument, which takes time to settle in simply because it seems so shocking at first. But Kinsella makes his case with powerful logic and examples that are overwhelming in their persuasive power.