Estonia has become the 17th country to adopt the euro, despite a crisis in the currency club.
The small Baltic state began to switch from its kroon currency to the euro at midnight local time after official celebrations in the capital Tallinn.
The switch marks the culmination of the country's successful transition from a former Soviet state, which regained its independence in 1991.
The kroon will be converted at the rate of 15.6466 at which the currency was pegged to the euro.
They will circulate together as legal tender for two weeks.
Estonia will be the currency club's poorest member but its debt and deficit levels - the cause of the crisis for some current euro zone members - are among the lowest in the bloc.
