The Maastricht Treaty (a/k/a the "Treaty of Maastricht" or the "Treaty on Economic Union") created the Euro as Europe's single currency. The treaty was signed Feb. 1, 1992 and came into force Nov. 1, 1993, although the Euro didn't come into use until 1999.
The Treaty is posted, with amendments, on Europa, with related Protocols and declarations. More information is available on Europa's Treaty of Maastricht page.
The treaty was originally published in International Legal Materials, 33 I.L.M. 395 (1994).