Patent law is about creating economic incentives to innovate. It grants the inventors of new, non-obvious, and useful technologies time-limited market exclusivityover their inventions. The idea behind this mechanism is to make socially desirable inventive activity privately profitable. As long as the invention withstands the patentability criteria, the inventor’s contribution to technological progress is believed to justify the social costs associated with market exclusivity, such as premium prices, reduced variety, and deadweight losses. Yet, as several scholars note, today many registered patents embrace technologies that would likely fail to withstand the legal patentability requirements. Notwithstanding their doubtful validity, weak patents exert a significant market influence, allowing their owners to stop other firms from using similar technologies or to extract fees for such use. These practices impose significant costs on the public, without justification in terms of contribution to technological progress. This Article identifies a basic flaw in patent law the asymmetry of risk allocation. The system is predisposed in favor of patent holders and against alleged infringers. This asymmetry gives much bargaining power to patent owners and invites opportunism. This Article proposes to reconsider the basic risk allocation in patent law and to introduce liability for damages caused by invalid patents.