This paper studies the early history of the idea of markets for emission rights in the late 1960s. It stresses the difference between Thomas Crocker’s and John Dales’s proposals that are rarely distinguished in the literature. It briefly presents Dales’s proposal and his important critics of optimal solutions, like cost benefit analyses, that led him to settle on a politically chosen level of emission. Finally, the paper shows that, even though today what are called cap-and-trade instruments are widely used to manage pollution, acid rain or global warming, the early reception of Dales’s idea by environmental economists was quite cautious, even by those who were promoting the use of incentives in pollution control.