Croatian leaders have presented a formal application to join the EU to the Greek Prime Minister, Costas Simitis.
Croatia is hoping to join the EU in 2007
"With this act Croatia is formalising its strategic goal of becoming an integral part of this new political entity," said Croatian Prime Minister Ivica Racan in Athens.
Greece currently holds the EU's rotating presidency.
Croatia, a country of 4.4 million people, won independence from Yugoslavia in 1991 but then fought a four-year war with its rebel Serb minority.
It remained isolated during the nationalist
rule of late President Franjo Tudjman, who died in late 1999.
Europe is certainly our goal, but it's also our fate, so let's take our fate into our hands
Croatian President Stipe Mesic
Apart from Slovenia, which is among the first ex-communist countries due to join the bloc in 2004, Croatia is the only other former Yugoslav republic to apply to the EU.
"United Europe is an unprecedented challenge of the new era and Croatia has a right to participate in this magnificent process," Racan said.
Croatia is aiming to meet strict criteria for entry and complete negotiations by 2006, paving the way for accession with Bulgaria and Romania in 2007.
The application has been released on a CD-Rom, which contains details on efforts to fulfil membership conditions.
Under the title "Re: member Croatia", it also includes speeches by President Stipe Mesic and Prime Minister Ivica Racan and a tourism video.
'More to do'
Mr Racan said that Croatia had come a long way in recent years, but still had a long way to go.
"We don't have illusions - we have to do more," he said.
"Croatia has changed, but the EU has changed as well. But there is no 'other' Europe, and we want to be in that company and share European values."
"Europe is certainly our goal, but it's also our fate," said President Mesic. "So let's take our fate into our hands."
Croatia has improved ties with the EU since Tudjman's death in December 1999.
But EU officials have warned that more needs to be done to meet preconditions for joining.
These include co-operation with the war crimes tribunal in The Hague and allowing the return of ethnic Serbs who fled during and after the war.