The aim of this article is to show Mundel.l's contribution to the theory of optimum currency areas. After an exposition of the contents of his 7.961 article, in which he explains the factor mobility criteria for the identification of optimum currency areas, the development of the theory in the sixties is presented, which mainly coinsits of the contributions of McKinnon (the openness criteria) dnd Kenen (the diversification criteria). This is followed by an overview of the more recent developments of the theory (endogenous criteria , criterie of homogeneolls preferences, etc.) and of the results of (he empirical work which it inspired.