The European Monetary System (EMS) was a multilateral adjustable exchange rate agreement in which most of the nations of the European Economic Community (EEC) linked their currencies to prevent large fluctuations in relative value. It was initiated in 1979 under then President of the European Commission Roy Jenkins as an agreement among the Member States of the EEC to foster monetary policy co-operation among their Central Banks for the purpose of managing inter-community exchange rates and financing exchange market interventions.

The EMS functioned by adjusting nominal and real exchange rates, thus establishing closer monetary cooperation and creating a zone of monetary stability. As part of the EMS, the EEC established the first European Exchange Rate Mechanism (ERM) which calculated exchange rates for each currency and a European Currency Unit (ECU): an accounting currency unit that was a weighted average of the currencies of the 12 participating states. The ERM let exchange rates to fluctuate within fixed margins, allowing for some variation while limiting economic risks and maintaining liquidity.

The European Monetary System lasted from 1979 to 1999, when it was succeeded by the Economic and Monetary Union (EMU) and exchange rates for Eurozone countries were fixed against the new currency the Euro. The ERM was replaced at the same time with the current Exchange Rate Mechanism (ERM II).