50 years ago, Alfrey and Price advanced the e-e scheme for the interpretation of radical and monomer reactivity and the prediction of monomer reactivity ratios in radical copolymerization. Despite the early criticism of the scheme by Mayo and Walling, and its obvious fundamental shortcomings, it continues to be essentially the only such scheme in use today. However, the more soundly based Patterns of Reactivity Scheme, originally proposed in 1959, has recently been revised in such a way that it provides, in a simple way, far more accurate predictions of monomer reactivity ratios than does the e-e scheme. Moreover, it is equally applicable to the forecasting of chain-transfer constants and to the understanding of the reactivity of initiator radicals. The history of investigations of radical, monomer, and transfer agent reactivity is reviewed here, including a summary of the Revised Patterns Scheme and its applications.