The right to mint coins is a royal right. Monaco has the right to mint coins like any other sovereign State. Prince Honoré II reaffirmed this right in 1612. The coins were first issued in 1640. Since the French alliance in 1641, Monegasque money must have the same value and be the same size as French coins. Monegasque money is legal tender in France.
When the euro came about, the Principality had the right to issue 1/500th of the money supply issued in France. This integration of the Principality into the euro zone, provided for by a declaration in an annex of the Maastricht treaty in 1993, was formalised by an agreement in 2001.