Ronald Coase's 1960 article, “The Problem of Social Cost,” has been one of the most influential works in the development of welfare economics since A. C. Pigou's The Economics of Welfare. Principally, the article made the definition and distribution of property rights a central issue when discussing the efficiency problems of negative externalities. Coase's approach has given rise to most of the economics of tort law and alternative liability rules. It has also led to the development of the “property rights” approach to environmental economics that has found prominence as an alternative to traditional Pigovian analysis.