“The Neoclassical Twain” tracks the tendency of Twain to be appropriated as a commentator on economic theory, history, and policy. I show that it has been particularly common for economists and economic journalists to cast Twain as an anticapitalist muckraker. The basis for such characterization is generally The Gilded Age, as well as some of his pre-1873 journalism. In this essay, however, I trace Twain's evolving positions on political economy through the two sequels to The Gilded Age, “Colonel Sellers as a Scientist” (1883) and The American Claimant (1892). In these later works, Twain actually contrasts the economic positions common to canonical novelists of the Progressive era. He shows considerable appreciation for the neoclassical economic theory of the marginalists and even anticipates the hegemonic celebration of free enterprise in the late twentieth century.