This book builds on a long tradition of research on the role of extrapolation in various fields. To make it clear, extrapolation means that the future course of a time series is seen as depending only on past observations of this series. It seems reasonable to begin the discussion of earlier contributions on this topic with research from the field of economics. Here we can connect with the material already discussed in Chapter 1. Clearly, Irving Fisher (1930) stands out for initiating the explicit mathematical modeling of extrapolative expectations in his work on inflation expectations. Variations of this theme were proposed in the form of adaptive and regressive expectations. While the hypothesis of adaptive expectations is a special variant of extrapolative expectations, the notion of regressive expectations brings in the element of a long-term anchor for predicted values.1 Expectations are said to be regressive when they show a tendency to revert to a fixed value. In a more general use of this term, we will speak of a regressive tendency if expectations increase in an under-proportional way in response to an increase in the underlying variable (e.g., inflation). Clearly, expectations can combine the elements of extrapolation and regressiveness, and we will pursue this topic in the chapters to come.