Can IP rights be lost? That is, once IP rights are acquired, what-if anything-must owners do to keep those rights or risk forfeiting them. The answer varies widely across the IP landscape and has important consequences for follow-on innovation, competition, and the public domain. This article takes the first close look at forfeiture mechanisms throughout the five major IP regimes-utility patent, trade secret, copyright, design patent, and trademark. I demonstrate how IP forfeiture mechanisms (e.g., maintenance fees, monitoring obligations, and use requirements) have weakened or narrowed over time. Building on prior scholarship, I also delineate the important functions that IP forfeiture mechanisms serve. By forcing IP owners to decide if the cost and effort of maintaining IP rights are worthwhile, forfeiture mechanisms help eliminate low-value IP rights and enlarge the public domain, benefiting follow-on innovators and society at large. In addition, forfeiture mechanisms serve an important notice or signaling role by forcing owners to engage in acts that inform second comers about the existence and scope of IP rights. These functions are particularly important when it comes to functional or useful subject matter (e.g., innovations that make a product work). Given forfeiture's role and its problematic narrowing across the IP landscape, I suggest the need for reform-particularly in design patent and copyright law, two areas that increasingly cover functional subject matter but lack any forfeiture mechanism.
