Abstract: Firms may acquire innovative targets to discontinue the development of the targets' innovation projects in order to preempt future competition. We call such acquisitions ``killer acquisitions.'' We develop a parsimonious model and provide empirical evidence for this phenomenon in drug development by tracking detailed project-level development histories of more than 60,000 drug projects. We show theoretically and empirically that acquired drug projects are less likely to be continued in the development process, and this result is particularly pronounced when the acquired project overlaps with the acquirer's development pipeline and when the acquirer has strong incentives to protect its market power. We also document that alternative interpretations such as optimal project selection, organizational frictions, and human capital and technology redeployment do not explain our results. Conservative estimates indicate that about 7% of all acquisitions in our sample are killer acquisitions and that eliminating their adverse effect on drug project development would raise the pharmaceutical industry's aggregate drug project continuation rate by more than 5%. These findings have important implications for antitrust policy, startup exit, and the process of creative destruction.