This chapter starts with the standard economic classification of the functions of money, then broadens the analysis to consider other related functions. In economics textbooks, money is said to serve three purposes: as a means of payment, unit of account, and store of value. After briefly explaining these functions, we revisit five monetary reforms enacted in Europe in the last century, showing how the monetary functions have been affected by those reforms: Reichsmark stabilization of 1923; Deutschmark introduction in 1948; German monetary reunification of 1990; and the introduction of the euro in 1999 and euro banknotes in 2002. These examples show that when the continuity of these functions is severed, monetary instability may result. Next we consider the requirements necessary to a successful money. Among them are portability; indestructibility; homogeneity; divisibility; stability in value, and cognizability. After considering the relationship between money and the state, we discuss supranational monies and the extreme ideal proposed by early philosophers and some modern economists: a single money for the world. We conclude that disconnecting money from the state (or from polity in a broader sense) is technically possible but difficult in practice. Money without states and monies with a less-than-complete political entities attached are more likely to be fragile and subject to confidence crises.