This collection brings together both classic articles which have laid the foundations for the theory of optimum currency and the resulting empirical literature. Articles are presented in sections on the theory of optimum currency areas, empirical analysis of optimum currency areas, fiscal policies in a monetary union, the central bank in a monetary union, and issues of transition to monetary union. Most articles were originally published in the 1990s. The editor teaches international economics at the University of Leuven, Belgium.