This analysis highlights the importance of transactions between prior and subsequent innovators to permit valuable research to go forward across the boundaries of prior patent claims. In a recent article focusing on biomedical research,4 Michael Heller and I argue that too many patent rights on \u27upstream\u27 discoveries can stifle \u27downstream\u27 research and product development by increasing transaction costs and magnifying the risk of bargaining failures. Just as too few property rights leave communally held resources prone to overuse in a \u27tragedy of the commons\u27, too many property rights can leave resources prone to underuse in what Heller calls a \u27tragedy of the anticommons\u27. The greater the number of people who need ...