Croatia has become the 28th member of the European Union, with crowds joining celebrations in the capital Zagreb, BBC News reported.
Fireworks lit the sky as membership became effective at midnight (22:00 GMT), with President Ivo Josipovic describing the event as historic.
Croatia is the first new EU member since Bulgaria and Romania joined in 2007. It is 10 years since it applied. Croatia's split from Yugoslavia triggered a 1991-1995 war to secure its independence.
But with one in five unemployed and Croatia's national debt officially classed as junk, some Croatians feel joining an economic bloc with its own serious troubles will do little to improve their prospects.
The EU itself has given Croatia a clean bill of health – and praised reforms which improve the rule of law and tackle corruption.
