The new chairman of EU summits, former Polish Prime Minister Donald Tusk, says the EU needs unity and "ruthless determination" to end the economic crisis and counter the bloc's foes.In a veiled warning about Russia's actions in Ukraine, Mr Tusk said "history is back, and such times need leadership and political unity".
Mr Tusk has one of the EU's top jobs.
As European Council president he is in a powerful position to shape the EU's priorities and hammer out deals among the 28 member states' governments.
He was the choice of the centre-right European People's Party, the pro-integration bloc that won May's European elections.
The BBC's Europe correspondent, Damian Grammaticas, says that Mr Tusk, like EU Commission President Jean-Claude Juncker, is a tough political operator, unlike some predecessors at the helm of the EU who were more grey and technocratic.
Eastern perspective Mr Tusk is also the first politician from Eastern Europe to get such a key role.
The Ukraine crisis has revived tensions between Russia and many of its former communist neighbours, which were dominated by the Soviet Union during the Cold War.
Mr Tusk vowed to protect the EU's fundamental values of "freedom and unity" against threats "from both inside and outside".
He mentioned "Eurosceptics, questioning the EU's value" and said Europe had to "secure its borders" and support "those in the neighbourhood who share our values", in an apparent reference to Ukraine.
He also pledged to strengthen Europe's relations with the US, calling the transatlantic partnership "the backbone of the community of democracies".
His chairmanship will be in the spotlight at an EU summit on 18-19 December.
The job used to change hands every six months, but Mr Van Rompuy, a former Belgian prime minister, became the first permanent council president in 2009. The idea was to give more coherence and continuity to EU policies.
