David Cameron and Nick Clegg have unveiled the policy programme their coalition will follow to create the "radical" change they say the UK needs.
Mr Cameron said the "remarkable" document combines the best of the Lib Dem and Tory manifestos - even though policies on both sides have been axed.
He described it as a blueprint for a "radical, reforming government".
But Labour said the agreement raised more questions than it answered - and had just "papered over the cracks".
Prime Minister Mr Cameron shared a platform with his deputy Mr Clegg to launch the 34-page document, which has been put together in nine days.
It builds on the four-page deal produced during negotiations in the immediate aftermath of the UK election which resulted in a hung Parliament.
The document includes the agreements on policy areas such as banking, civil liberties, defence, the environment, Europe, immigration, welfare and political reform - some of which the parties have disagreed on in the past.
It includes plans to sell off at least part of Royal Mail, although it vows to keep the Post Office network in public ownership.
On crime, it promises to slash police bureaucracy and says people will be given "greater legal protection to prevent crime and apprehend criminals". A new border police force will be part of a "refocused" Serious and Organised Crime Agency. Anonymity in rape cases will be extended to defendants.
The sale of below cost price alcohol will be banned and councils allowed to charge more for late pub licences to pay for more police - although 24 hour drinking will not be scrapped.
The new government also pledges to freeze council tax in England for at least a year. The right to request flexible working will also be extended to all employees.
Both Mr Cameron and Mr Clegg said tackling Britain's record budget deficit would be their first priority but stressed that that did not mean they could not pursue a "radical" reforming programme of government.
In the document's foreword, the two party leaders write: "In every part of this agreement we have gone further than simply adopting those policies where we previously overlapped.
"We have found that a combination of our parties' best ideas and attitudes has produced a programme for government that is more radical and comprehensive than our individual manifestos.
"For example, when you take Conservative plans to strengthen families and encourage social responsibility and add them to the Liberal Democrat passion for protecting our civil liberties and stopping the relentless incursion of the state into the lives of individuals, you create a big society matched by big citizens."
At the joint press conference, Mr Cameron said the coalition had the "potential to be a great reforming government".
Rather than diluting policies, Mr Cameron said that in some areas, such as the NHS, the agreement was more "radical" than either the Conservative or Lib Dem manifestos, combining Tory belief in free markets with their coalition partners' commitment to decentralisation.
The prime minister said his government was "united behind the three principles of freedom, fairness and responsibility but also united in the purpose of bringing strong, stable, decisive government to our country".
Mr Clegg said the document - entitled Our Programme for Government - would "transform our country for the better".
He said the coalition's reform plans had been strengthened by the need for compromise and that it had the potential to provide stronger and more stable rule than a single party government.
He stressed that the Lib Dems and Conservatives would fight the next general election as separate parties but said that for the next five years would work in partnership to pursue a "radical, reforming" agenda.
'Value for money'
"Even if you've read 100 party manifestos, you've never read a document like this one," said Mr Clegg, who spoke first as Mr Cameron sat in the audience.
"Not one party's ideas, not even just two parties' ideas, but a joint programme for government based on shared ambitions and shared goals.
"Compromises have, of course, been made on both sides, but those compromises have strengthened, not weakened, the final result.
"From different political traditions - conservatism and liberalism - we've come together to forge a single programme drawing on the strengths and traditions of both of our parties."
Lib Dem policy chief Danny Alexander who hammered out the detail of the agreement with Conservative counterpart Oliver Letwin described it as a "blend of the best of the best of both parties in an agreement which is stronger, richer and more radical and reforming as a result".
The document confirms pledges to scrap the ID card scheme and national identity register, and introduce a Freedom Bill. There will also be a series of reforms to the political system including a referendum on a move to the Alternative Vote system for Westminster elections.
Britain's Trident nuclear weapons will be maintained but scrutinised to ensure "value for money" and the Lib Dems will continue to make the case against their renewal.
Lib Dem MPs will also be able to abstain from planning reforms that will make it easier to build nuclear power stations.
A series of commissions will be set up to investigate areas in which the two parties have failed to agree - such as scrapping the Human Rights Act and breaking up the big banks.
There will also be a review of the non-domiciled tax system, in place of the Conservative policy of a flat £25,000 a year rate and the Lib Dem policy of making non-doms pay the same tax rates as domiciled British citizens after seven years.
The coalition has adopted the Lib Dem proposal for a social care commission to consider how to fund the future needs of an ageing population. Tory plans for a voluntary insurance scheme are now described as one of a "range of ideas" to be considered.
There will be an annual limit on non-EU migration, in line with Tory policy, but no figure is mentioned and there is no mention of the Lib Dems' call for earned citizenship for illegal immigrants.
On Europe, there is a pledge of a referendum on the transfer of any further powers to the EU and a vow not to adopt the euro. But other key Tory pledges appear to have been watered down to accommodate the pro-European Lib Dems.
The Tory manifesto promised to introduce a Sovereignty Bill, to make it clear that "ultimate authority" remained in the UK - the coalition agreement says the government will merely "examine the case" for such a move.
And a Tory promise to restore national control over social and employment legislation has been replaced by a more nuanced commitment to "examine the balance of the EU's existing competences" and, in particular, to "work to limit" the application of the working time directive.
Conservative plans to scrap the so-called couple penalty in the tax credit system also appear to have been watered down, with the government document saying it will bring forward plans to "reduce" rather than "end" it, as the Tory manifesto promised.
There is no mention of a Lib Dem pledge to repeal the controversial Digital Economy Bill, passed in the dying days of the Labour government, and on the funding of high speed broadband the Conservative policy of relying on the market with possible help from the BBC licence fee, appears to have held sway over the Lib Dem landline tax proposal.
Giving his reaction to the new government's programme, former Labour minister Hillary Benn predicted it would not be long before fundamental policy disagreements emerged between the Conservatives and Lib Dems.
He told BBC News: "We will have the very strange spectacle of Lib Dem ministers able to stand up and oppose a policy on nuclear power - we need a balanced energy policy, including to fight climate change - while Tory backbenchers will get a free vote on bringing back animal cruelty to the countryside, because they want to bring back hunting with dogs. And that is certainly not my idea of the new politics."