The relationship between economics and psychology is described from the end of the 18th century to the present day. Three stages are identified: that of the first marginalist authors up to Pareto, the one characterized by the expected utility axioms proposed by von Neumann and Morgenstern, and the last phase due to the work of Simon and others from 1950 onwards. In this last stage, the two main research programs are described: the “biases and heuristics” (Kahneman and followers) and the “ecological rationality” (or also “fast-and-frugal heuristics”) (Gigerenzer and colleagues). Finally, the types of experiments carried out in economic psychology are explained.