THIS paper asks whether the principal doctrines of products liability law are consistent with the hypothesis that the common law is best understood as an endeavor (which need not be conscious) to promote economic efficiency, taking the existing distribution of income and wealth as given.1 In contrast to most of the literature on products liability law, we emphasize positive rather than normative analysis, and we even offer some empirical analysis-a rarity in this field. Heavily criticized as a willful interference with the free market in goods and services,2 modern products liability law seems at first glance a powerful contradiction to the efficiency model. We shall argue, however, that both the historical development of the law and its current doctrinal structure are in the main consistent with efficiency. We emphasize this qualification. We shall not try to explain every decision-there are thousands every year. We shall not consider the day-to-day administration of the law, or even every doctrinal twist and turn-in fact, we identify several doctrines that are anomalies from an economic standpoint. We shall not discuss all the major doctrines of this immense field, an undertaking too ambitious for a single paper.