This talk by Issac Deutscher was originally published in Monthly Review on December 1967 to commemorate the 100^th anniversary of Karl Marx’s Capital. We are making it available here on the occasions of the 150^th anniversary of Capital. In the original editors’ note to this article, 50 years ago Leo Huberman and Paul M. Sweezy wrote: “This is the text of a talk given last summer on the BBC’s Third Programme. It is reproduced here by permission. Isaac Deutscher is the author of distinguished biographies of Stalin and Trotsky, and at the time of his death at the age of 60 last August he was working on a biography of Lenin.” —The Editors