The formation of expectations and the issue of efficiency are of prime importance to economic researchers and market participants alike. The Rational Expectations Hypothesis (REH) is a powerful analytical tool for examining the formation and consequences of expectations in economic activity. Another is the Efficient Markets Hypothesis (EMH): a market is said to be informationally efficient if prices in that market reflect all relevant information as fully as possible. In his introduction the editor surveys recent research on these two hypotheses, while the contributors present new theoretical and empirical analyses of these issues and of the common ground between them.