Monopoly Capital
Baran introduced the concept of "economic surplus" to deal with novel complexities raised by the dominance of monopoly capital. With Paul Sweezy, Baran elaborated the importance of this innovation, its consistency with Marx's labor concept of value, and supplementary relation to Marx's category of surplus value. Monthly Review has recently published a book of correspondence between Sweezy and Baran, which illuminates the development of their ideas on political economy, and in particular, their collaboration in writing their seminal work, "Monopoly Capital". See "The Age of Monopoly Capital, The Selected Correspondence of Paul A. Baran and Paul M. Sweezy, 1949–1964", edited by Nicholas Baran and John Bellamy Foster, Monthly Review Press, New York, 2017.