In which treaty was the agreement to form a European monetary union formalized?

The agreement to form a European monetary union was formalized in the Maastricht Treaty, which was signed in 1992. This treaty laid the groundwork for the creation of the euro and the establishment of a single currency among European Union member states. It introduced the convergence criteria that countries needed to meet to adopt the euro and outlined the institutional framework for the European Central Bank. The Maastricht Treaty is a cornerstone of European economic integration, marking a significant step towards deeper political and economic unity in Europe.

The other treaties listed do not pertain to the establishment of a monetary union. The Paris Summit in 1976 focused on various political and economic issues but did not create a monetary union, while the Amsterdam Treaty in 1999 dealt mostly with institutional reforms. Milan does not pertain to this context at all, as there was no significant treaty concerning the European monetary union signed there.