The Treaty of Lisbon was signed on 13 December 2007 between 27 European states that are members of the European Union (EU). It became effective on December 1, 2009. It is now the document that defines the Union, but it is not a constitution. It gives a common set of rules that the member states have agreed to use on subjects where they have decided to work together. It does better than previous treaties such as the Treaty of Rome and the Treaty of Maastricht. It gives the European Union new things, such as:

• a President of the European Council (who is not the President of the European Union – there is no such job).
• a High Representative for Common Foreign and Security Policy, who is a member of the European Commission and who represents the Union around the world.
• stronger role for the European Parliament, which is directly elected by citizens of the EU,
• the ability to make more decisions by "qualified majority". Although some decisions require that all member states agree, there are more that can be decided if there is a large majority.
• better police and justice across the continent.