This paper is concerned with the fact that the incidence of speculative attacks tends to be temporally correlated; that is, currency crises appear to pass contagiously from one country to another. The paper provides a survey of the theoretical literature, and analyzes the contagious nature of currency crises empirically. Using thirty years of panel data from twenty industrialized countries, we find evidence of contagion. Contagion appears to spread more easily to countries which are closely tied by international trade linkages than to countries in similar macroeconomic circumstances.