This Article provides a framework for reconciling the tension between tort doctrine and economic theory, and for addressing the general failure of economically oriented theories to come to grips with doctrine at a detailed level. My claim is that tort doctrine should be viewed as a response to the incompleteness of markets, or more generally the problem of missing markets. Because of market incompleteness, some of the benefits as well as costs associated with activities will be shifted or externalized to third parties. Tort doctrine reflects sensitivity to the externalization of benefits and costs. It can therefore be understood only by examining both types of externalization. I provide a framework that explains pockets of strict liabilit...