This article investigates the origins and early development of the association between the efficient market hypothesis and rational expectations. These two concepts are today distinctive theoretical benchmarks for mainstream approaches to, respectively, finance and macroeconomics. Moreover, scholars in each of these two fields tend to associate the two ideas as related equilibrium concepts; they also claim that the two have a common historical origin. Although some historical accounts have been provided about either the origins of rational expectations or of the efficient market hypothesis, very few historians have been investigating the history of the association between the two concepts (or, more generally, the history of the interactions between macroeconomics and finance). The contribution of this paper is precisely to fill this gap in the historical literature, while assessing and challenging self-produced narratives told by practitioners. We suggest that the two concepts were independently developed in the 1960s. Then, we illustrate how they were associated for the first time the early 1970s, within a debate about the term structure of the interest rates involving Sargent, Modigliani, Shiller, and Fama. Finally, we discuss some early controversies about the association, which nevertheless became, at the turn of the 1970s, a step-stone for both macroeconomics and finance.