All EU countries must ultimately join the euro area as their currency, except Denmark which has negotiated an opt-out. To adopt the euro as their currency, countries must meet certain criteria. They must have price stability, sound public finances, a sustainable long-term interest rate and a stable exchange rate.
A country takes on responsibilities too when it applies to adopt the euro. It has to permanently fix the exchange rate between its national currency and the euro. Once the country is a member of the euro area, it transfers responsibility for its monetary policy to the European Central Bank. It is also expected to coordinate with other euro area countries on crisis management, including providing financial assistance to them when needed, to ensure stability.
Governments have to inform their citizens about the changes that come with joining the euro area to help them prepare. Every year, they submit their draft budgetary plans for the following year to the Commission for assessment; they can be sanctioned if they fail to comply with the criteria on sound and sustainable public finances.