Czech president Vaclav Klaus has signed the Lisbon Treaty reforming the European Union, removing the last obstacle to it coming into force.
It follows a ruling by the Czech constitutional court that the treaty did not conflict with the country's laws.
Among its measures, the treaty creates a European Council president and alters the way member states vote, the BBC reports.
National vetoes would become the exception rather than the rule in most policy areas.
Its supporters say it will allow the EU to operate more efficiently and give it greater influence in world affairs while critics say it will cede too many national powers to Brussels.
The Lisbon Treaty could now come into force as early as December.