Disagreements over trade, energy, human rights and international affairs look set to dominate the EU-Russia summit near the Portuguese capital, Lisbon.
It is the last one that Vladimir Putin is due to attend as Russian president before he steps down next year.
EU officials are hoping to ease the increasingly strained relations between the bloc and Russia.
But ahead of the summit, rights groups have urged the EU to challenge the Kremlin over its human rights record.
The setting for Vladimir Putin's last summit with EU leaders could not be more uplifting - a huge, baroque convent, under an almost cloudless sky.
There is modest hope that the political mood will be slightly less chilly at the end of the day.
New self-confidence
The EU depends on Russia for a third of its energy needs and after two successive winters where gas supplies were disrupted it will welcome a deal on an early warning system to avoid future crises.
There is also a renewed self-confidence among EU leaders following the conclusion of a new reform treaty last week and the electoral defeat of Poland's nationalist government which had been blocking talks on a new wide-ranging agreement with Moscow.
But continuing concerns over human rights and democracy will overshadow the summit, ahead of Russia's parliamentary and presidential polls.
In separate appeals, both Human Rights Watch and Amnesty International have urged EU leaders to speak firmly and with one voice about what the groups call the Kremlin's worsening human rights record.
They will be closely watching the Portuguese Prime Minister, Jose Socrates, the host of the summit, who earlier this year said he would not lecture Russia.
(BBC News)