Originally published in 1979. This book addresses three questions regarding uncertainty in economic life: how do we define uncertainty and use the concept meaningfully to provide conclusions; how can the level of uncertainty associated with a particular variable of economic interest be measured; and does experience provide any support for the view that uncertainty really matters. It develops a theory of the effect of price uncertainty on production and trade, takes a graphical approach to look at effects of a mean preserving spread to create rules for ordering distributions, and finishes with an econometric analysis of the effects of Brazil’s adoption of a crawling peg in reducing real exchange rate uncertainty. This is an important early study into the significance of uncertainty.