British Prime Minister David Cameron has negotiated a series of reforms to his country's relationship with the European Union, ahead of a referendum on membership expected to take place later this year.
Britain has always been reserved about its place in the 28-member bloc, with euroscepticism growing in recent years.
The reforms, agreed after marathon talks in Brussels, are legally binding and can only be changed by unanimous agreement of all member states. They will only come into effect if Britons vote to remain inside the bloc.
Key aspects of the deal:
Britain has secured recognition that it is not committed to further political integration into the EU. The country has argued that it does not want to surrender more powers to Brussels.
References in EU treaties "to ever closer union do not apply to the United Kingdom," the text states. Wording to this effect is to be included in future treaty changes.
Cameron had also wanted to give national parliaments a greater say on EU issues.
The leaders agreed to a "red card" system that will allow 55 per cent of national parliaments to club together and stop or amend newly proposed EU legislation, if they believe the matter should be dealt with nationally.
SOCIAL BENEFITS/FREE MOVEMENT
Cameron's efforts to curb labour immigration proved particularly thorny. Many Britons fear that continental Europeans are saturating their job market and abusing the country's welfare system.
Under the deal, Britain can apply a "safeguard mechanism" that will restrict incoming workers' access to social benefits for four years, gradually raising entitlements over this period. Other member states will have to approve the measure, which can then apply to newly arrived workers for seven years.
Another point of contention was a British bid to reduce child benefits to EU workers whose families live abroad.
EU leaders agreed to let any member state adapt child benefits for these workers to costs in the country where their family is living. Under the compromise, this will apply only to new claims until 2020, when it can be extended to previously existing child benefit payments.
The text includes wording to prevent this system from being extended to other benefits such as pensions.
Britain, which is home to the EU's largest financial hub, is worried that decisions taken by eurozone countries could harm its interests. London has no plans to ever adopt the euro.
In response, the leaders approved a mechanism to address the concerns of non-euro states, allowing them to trigger debates among the 28 EU leaders on initiatives that they believe harm their interests.
However, the mechanism "cannot constitute a veto nor delay urgent decisions," EU President Tusk has said.
Britain has been granted assurances that the EU will seek to improve its competitiveness, cut red tape for businesses, pursue an ambitious trade policy, encourage entrepreneurship and boost job creation.
Many people in Britain view the EU's single market - in which goods, people, services and capital can move freely - as one of the most attractive aspects of membership.