Will all EU countries adopt and use Euro as main currency ?

Do all the EU member countries must adopt and use Euro as their official currency in the future ? Are there any exceptions ?

According to the Maastricht Treaty EU members are obliged to adopt euro in the future, upon meeting certain monetary and budgetary convergence criteria, but not all the member states have to do so. Denmark and United Kingdom negotiated exemptions, so they keep using their own official currencies.

It usually takes longer period of time to meet the convergence criteria, because the adoption of Euro requires economic stability.