''Lex monetae'' is a

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

phrase which means that a sovereign state chooses which

currency A currency, "in circulation", from la, currens, -entis, literally meaning "running" or "traversing" is a standardization of money in any form, in use or circulation as a medium of exchange, for example banknotes and coins. A more general ...

it will use and that the meaning of units of above-mentioned currency is determined by the law of the country whose money is in question. The concept has been identified as a potential problem if the

Eurozone The euro area, commonly called eurozone (EZ), is a currency union of 19 member states of the European Union (EU) that have adopted the euro ( €) as their primary currency and sole legal tender, and have thus fully implemented EMU polici ...

breaks up or a member state decides to leave it, since debts in

euro The euro ( symbol: €; code: EUR) is the official currency of 19 out of the member states of the European Union (EU). This group of states is known as the eurozone or, officially, the euro area, and includes about 340 million citizens . ...

s may turn into debts owed in another currency. Conversion would be at a rate determined by the nation in question, and no party to a contract or transaction will have the right to default on it. In 2016, Jacques Sapir asserted that "public debt issued under French law (which corresponds to 97% of the amount of this debt) must be repayable in the currency that is legal tender in France"..

References

Currency Latin words and phrases {{italic title