‘The market makes its money’, thought Hicks, and similar messages have been delivered by many other thinkers on money. However, while students of money have mostly been concerned with who could or should produce it, the market or the state, few have questioned whether the money itself should be single or not. Apparently it has been taken for granted that a single market and a single money should coincide. Nevertheless, contrary to the modern assumption that one single currency should operate in one country, the history of money has been full of plurality until recent times, as we will argue in this issue. It is no exaggeration to say that the majority of human beings through most of history dealt with concurrent currencies. It is important to recognise that, in most if not in all cases, the coexistence of monies was not incidental but functional, since they worked in a complementary relationship. That is, one money could do what another money could not, and vice versa. In other words, an assortment of monies could do what any single money could not, and supply what the market required. In the following articles we will show how this worked.