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 on Sunday with President Ivo Josipovic describing the event as historic. It comes almost two decades after Croatia's brutal war of independence.
But enthusiasm for the EU in the country has been dampened by the eurozone crisis, and Croatia's own economic problems, the BBC reports.
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."
Croatian officials unveiled EU signs and removed customs posts at the borders with Slovenia, the first former Yugoslav republic to have joined the bloc, and with Hungary.
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.