France and the Netherlands said they would be unable to adopt the constitutional treaty without significant changes, following the 2005 referendums.
The UK also pressed hard for a modest "amending treaty", which could be ratified by means of a parliamentary vote, like earlier EU treaties.
Does the Charter of Fundamental Rights feature in the new treaty?
No. There is a reference to it, making it legally binding, but the full text does not appear, even in an annex.
The UK has secured a written guarantee that the Charter cannot be used by the European Court to alter British labour law, or other laws that deal with social rights. However, experts are divided on how effective this will be.
Poland won an opt-out from the Charter, because it insisted on retaining national control over family issues and morality, such as abortion.
The Czech Republic also has an opt-out - secured by the Eurosceptic Czech President Vaclav Klaus as a condition for signing the treaty. He wanted a guarantee that his country would not be exposed to property claims by Germans expelled from the then Czechoslovakia after World War II.
Did any countries seek more opt-outs?
The Irish Republic and the UK currently have an opt-out from European policies concerning asylum, visas and immigration. Under the new treaty they have the right to opt in or out of any policies in the entire field of justice and home affairs.
Dublin also won guarantees that the treaty would not infringe on its sovereignty in the areas of taxation, family issues and state neutrality.
Denmark will continue with its existing opt-out from justice and home affairs, but has the right under the new treaty to opt for the pick-and-choose system.
Was the Irish Republic the only country to hold a referendum?
Yes. Most EU leaders argued that Lisbon merely amended earlier treaties and that there was therefore no need for a referendum.
That position was rejected by the Irish No camp and the opposition Conservative Party in Britain, as well as by many Eurosceptics across the EU.
The Irish Republic was obliged to hold a referendum because of an Irish Supreme Court ruling in 1987, saying that any major amendment to an EU treaty entails an amendment to the Irish constitution.
Before the second Irish referendum, Dublin won guarantees that Lisbon would not affect Irish sovereignty in key areas that the No camp had highlighted.
What happens next?
• The High Representative for Foreign Affairs - Baroness Catherine Ashton from the UK - is getting to grips with the EU foreign policy portfolio. Her new EU diplomatic service is taking shape, drawing in specialists from the Commission and national administrations;
• The new President of the European Council - Belgium's Herman Van Rompuy - is chairing EU summits, though many EU ministerial meetings are still being chaired by the country holding the six-month presidency - currently Hungary;
• The new European Parliament was elected in June 2009 under the existing Nice Treaty. So there are 736 MEPs - down from the previous 785. Under the Lisbon plan, the number will be fixed at 751;
• A new 27-member European Commission took office in February 2010, after a three-month delay, having won the backing of MEPs;
• Some extensions of qualified majority voting in the European Council are already in place, but plans to redistribute voting weights have been delayed until after 2014.