The debate on the optimum size of farms is very old, dating back at least to the end of the 19th century, when most experts believed that ultimately agriculture would be like any other sectors of the economy and many authors spoke of the industrialization of agriculture. But subsequently that view was more and more challenged. And in the 1960s, a broad consensus emerged among professional economists, particularly those concerned with economic development, on the superiority of small family farms. The debate appeared settled. Yet several developments in recent decades - notably the existence of very large farms in countries of the former Soviet Union, the forms taken by what is commonly called “land grabbing” in Africa, the economic dynamism of large commercial farms in several Latin American countries - have put the consensus on the superiority of small farms into question. The purpose of this essay is to review this old debate, to show its great policy relevance today and to suggest that public policies supporting small farms continue to be warranted today, as situations vary greatly among countries and among regions. Strategies targeting small family farms that can produce for the markets, i.e., beyond subsistence needs, and be linked to value chains are of primary importance, for social as well as economic reasons.