Single European Act, SEA
The Single European Act is the name of an EU treaty.
The SEA, signed in 1986, entered into force in 1987 after referenda in Denmark and Ireland. Together with the Treaty of Maastricht, it has introduced the most extensive changes to the treaties so far.
It introduced qualified majority voting around the internal market making it possible to adopt around 300 laws implementing the single market. It also introduced the co-operation procedure giving the EU Parliament the possibility of putting forward amendments to a part of the legislation.
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See also Environmental clause, internal market and Cassis de Dijon Case.