Croatia has become the 28th member of the European Union, with crowds joining celebrations in the capital Zagreb.
Fireworks lit the sky as membership became effective at midnight (22:00 GMT), with President Ivo Josipovic describing the event as historic.
It comes almost two decades after Croatia’s brutal war of independence.
But correspondents say enthusiasm for the EU in the country has been dampened by the Eurozone crisis, and Croatia’s own economic problems.
Celebrations took place in the central square of Zagreb, with fireworks and music including Beethoven’s Ode to Joy, the European anthem.
“Welcome to the European Union!” European Commission President Jose Manuel Barroso said in Croatian to the cheering crowd.
President Josipovic said it was “a great and joyful day for our homeland”.
“This the day when we open a new chapter in the thick book of our history,” he added.
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