Bruno de Finetti (1906–1985) is well known as the founder of the subjective theory of probability. Less known is his contribution to economic theory. The article presents the contributions of de Finetti in the field of welfare economics. He advanced a new mathematical tool: the theory of simultaneous maxima. On this base, he criticized the laissez-faire interpretation of the Paretian theory and advanced the idea of a social welfare function, reflecting the debate on economic planning among Italian corporatist economists.