A form of currency which was accepted by mutual agreement at a fixed standard within certain boundaries. In ancient times uniform types are found on the coins of the Achaean League, originally formed in the fourth century B.C. by some cities on the Corinthian Gulf. All these issues have AX or AXAIQN, the mark of the League, and over forty cities joined it before it was dissolved. The example was copied by the Aetolian, Boeotion, Ionian, and other Leagues.

The Electors of Cologne, Trier, Mainz, and the Palatinate made an agreement in the fourteenth and fifteenth centuries by which their gold florins were struck of a uniform weight and value. Other important monetary conferences were those of various cities in the Low Countries in the fifteenth century; the coinage of the Protestant Rulers during the Thirty Years' War ; the Convention of 1753, legalizing the Species Thaler; the one of 1865, called the Latin Union, in which the Franc, Lira (and later the Drachma and Peseta) were put on the same basis ; and lastly the Scandinavian Conference of 1872 between Sweden and Denmark, to which Norway became a party in 1877.

The Tallero di Convenzione, struck for Venice under Francesco I (1814-1834) and later, had a value of three Lira. The term Vereins Thaler is frequently found on the coins of Leopold Friedrich of Anhalt- Dessau (1817-1871), and Alexander Carl of Anhalt-Bernburg (1834-1863).