It's an uphill task, and diplomatic victory is far from certain, but Cameron hopes to come away from the initiative taller and stronger in the eyes of his Conservative electorate.
No one denies the EU is in need of sweeping reforms but key players France and Germany don't want Britain to be that instigator of change.
The EU is beset with huge financial and political problems, not least the failing rescue package for tiny member Cyprus in the eastern Mediterranean, which seems to be in the need of yet another cash bailout after claims the last handout wasn't enough to ease its misery.
Cameron took his family to German Chancellor Angela Merkel, the EU's uncrowned supremo, in a thinly disguised private visit where the two are to look at ways in which Britain can stay in the EU without causing too much disruption.
British noises over EU profligacy and lack of accountability of its largely unelected administration have won London few friends in Brussels or even Berlin but have given Berlin cause of concern amid fears the contagion of discontent emanating from London may spread to other disaffected members.
Several EU members are said to be supportive of British calls for EU structural reform but are afraid to side with London for fear of displeasing Berlin or losing privileges.
Increasingly the EU and eurozone project has become a German project with emphasis on success at all costs. In the Cyprus rescue package EU chose to sacrifice Cypriot depositors, with unprecedented provisions of levies on high-value depositors, rather than let Cyprus fail and trigger a sovereign default.
Cameron aides say the prime minister believes the EU needs to change to allow Britain and several other dissenting members not to be bound by all of its decisions.
Cameron was accompanied on the visit by his wife Samantha and their three children, following a personal invitation from Merkel.
Cameron is also hoping to attempt similar diplomacy in Paris, after a false start when he had to cancel a visit to French President Francois Hollande because of preparations for the funeral of late prime minister Margaret Thatcher.
Cameron's Conservative Party aides say the prime minister is still intent on holding a referendum on Britain staying within the EU. Critics say the government's jockeying for position on the issue is for popular conservative consumption in Britain.
Speaking of Britain's future in Europe earlier this year, Cameron pledged to hold an in-out referendum during the early part of the next Parliament or by the end of 2017 at the latest if the Conservatives stay in power.
British businesses have called Cameron's position reckless and warn that a departure from the EU will wreak havoc on British economy and society.
Cameron has said Britain's "membership of a reformed European Union" could be the best outcome for the country. Neither France nor Germany have indicated they want the EU to concede to Britain on any point
Cameron said the EU "sometimes overreached itself with directives and interventions and interference." Critics say that's the kind of language Cameron's Conservative backers want to hear.
"I think we can have a flexible Europe where we don't all have to do the same things in the same way at the same time," Cameron said. It's by no means certain that anyone in the EU will accede to British demands as there's lingering fear acquiescence to London will trigger copycat reactions from some of the other EU members.
Last year British Foreign Secretary William Hague launched a "comprehensive audit" of European Union powers and their impact on the U.K. Critics of the government see the audit as little more than a political gimmick by Cameron's Conservative Party.