In the two decades following Douglas’s presidential address to the AEA, the Cobb–Douglas regression came to be a familiar and widely used tool in empirical economics. Part II of this book explores this diffusion process, mainly by means of two case studies: the first describing how the regression was adopted by researchers in agricultural economics and the second looking at the uses to which the regression was put by economists seeking to measure and explain economic growth. First, however, I provide some necessary background for the case studies by reviewing three general developments that affected economists’ perception and use of the regression in the 1950s and 1960s.