AbstractThe essay investigates the parallels and connections between Friedrich A. Hayek and Ronald H. Coase. It emphasizes the shared context at the London School of Economics (LSE) in the 1930s within which both authors reacted, in particular the role of the so-called LSE tradition on opportunity cost. We focus attention on the same pattern of institutional reaction to the formal similarity proposition of neoclassical general equilibrium theory exposed in both authors. In “The Nature of the Firm” (1937a), Coase’s pioneer transaction cost argument was decisively constructed and shaped by the controversy around the possibility of rational economic calculation under socialism. This debate was crucial to Hayek’s fundamental reformulation of neoclassical equilibrium analysis in terms of a social coordination problem in “Economics and Knowledge” (1937). In a parallel manner, although focused on the microstructure of production, Coase (1937a) was reacting to the standard general equilibrium theory and its postulates. Traditional microeconomic theory could not explain the decisions to make within the firm or to buy in the market, nor the many hybrid organizational arrangements that lie between the centralized firm and the decentralized market process. In “The Problem of Social Cost” (1960), Coase develops his argument advanced in 1937 to the welfare corollaries of the general equilibrium framework encapsulated in the first and second welfare theorems. In this case, the connection was made through the influential ideas of his long-LSE friend, Abba P. Lerner. Finally, the essay explores Hayek’s instrumental role in the intellectual and institutional foundations of the Law and Economics movement at the University of Chicago.