Thorstein Veblen is noted for his view that economics should be an science. However, although the term has been adopted in general terms by subsequent institutional economists, there has been remarkably little detailed exploration, informed by biology, of what Veblen meant by an science and the character of the post-Darwinian economics that he attempted to build. This essay explores the reasons for Veblen's attachment to Darwinism, informed by developments in biology itself, and identifies some distinctive and enduring features of Veblen's evolutionary theory. Copyright 1992 by Oxford University Press.