Dumping actions and anti-dumping policies were regularly on the political agenda for several years in the pre-World War I period in Europe and the United States. In Italy, politics, economic circles, and scholars were engaged in debate on whether to protect sensitive industries threatened by sales below cost in their home markets, practiced by foreign competitors. Einaudi and his school of economics tackled the issue with several publications. In this paper we focus on Jannaccone’s essays, which he contributed to both a symposium in Riforma sociale in March 1914 and an issue in Rivista delle società commerciali in June 1914. Although we recognize that Viner (1923) theoretically systematized dumping in the wider framework of international trade, we nevertheless claim that the theoretical origin of dumping, in a context of imperfect competition, was Jannaccone’s essay. We show that Jannaccone proposed an early theory of dumping as an instance of the more general theory of price discrimination. He defined and classified dumping; he developed a static analysis of its profitability; he investigated the effects of dumping in both domestic and foreign markets; and he analyzed the effect of protectionism and its policy implications.