This is a somewhat extended and edited version of a paper presented at a three-day colloquium on the general subject of "Value Theory and Contemporary Capitalism" which took place in London in November 1978 under the joint auspices of the New Left Review, the Cambridge Journal of Economics, and the Conference of Socialist Economists, which publishes the journal Capital and Class. At the center of many of the discussions were the ideas set forth in the recent book by Ian Steedman, Marx After Sraffa (London: New Left Books, 1978). Steedman was also one of the principal speakers and an active participant in the discussions at the colloquium. - P.M.S.This article can also be found at the Monthly Review website, where most recent articles are published in full. Click here to purchase a PDF version of this article at the Monthly Review website.