The European Union has launched its mission to strengthen the rule of law in Kosovo, after months of delay, according to BBC.
Some 2,000 officials are taking over police, justice and customs duties from the United Nations staff.
Serbia rejected Kosovo`s declaration of independence in February and still regards Kosovo as one of its provinces, but it has accepted the new EU mission.
The UN will leave Kosovo after more than a decade in charge, retaining only a small political role.
Eulex is the EU`s biggest-ever mission and will operate across all of Kosovo.
The EU will oversee the running of the police, the courts and the customs service.
The aim is to help the authorities deal with corruption and organised crime, the BBC`s Helen Fawkes in Pristina says.
Plagued by delays
The mission is a huge test for the EU, says political analyst Lulzim Peci:
"If you succeed here, then you can prove to be capable to be engaged in other crises. But if you fail in Kosovo... then you lose credibility for overseas operations."
Already there have been problems, our correspondent says.
Eulex was supposed to have started months ago but it was plagued by delays and opposition from Serbia.
Belgrade has now accepted the plan, however many Kosovo Serbs are still unhappy that the UN is leaving.
There have also been protests by majority ethnic Albanians who believe that too many concessions have been made to Serbia.