On his first foreign trip since winning a general election earlier this month, Cameron is set to meet some of Europe's leading figures as he seeks to secure reforms over issues including immigration.
The Eastern Partnership summit in the Latvian capital Riga from tomorrow focuses on how the 28-member bloc should reconcile its commitment to six former Soviet states with its relationship with Russia.
But it will also signal the start of Cameron's renegotiation push, a painstaking process likely to last for months which the British leader says will require EU treaty change.
"The package of measures outlined will need treaty change," he said.
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Under pressure from eurosceptics, the British prime minister promised in 2013 to hold a referendum on whether Britain should leave Europe by 2017 if he won the general election.
Having secured victory on May 7 with a surprise though slender majority, he is now under pressure to hold the vote sooner rather than later.
Nigel Farage, leader of the anti-EU UK Independence Party which has been riven with splits since winning only one seat at the election, believes the referendum will be held in May next year.
Farage warned in comments on BBC Radio 4's Today programme of "a great stitch-up where the European Commission and the European Council are seen to give some cosmetic concessions to Britain.
"Mr Cameron cries victory, on the basis of that we're supposed to support him in the referendum," he said.