Single institutional framework

The single institutional framework is the practical expression of the principle that there is only one set of institutions. It presupposes that Member States wishing to integrate and cooperate still further will agree to act through shared institutions. It also requires the other non-participating Member States to accept that shared institutions can be used for such operations to knit the Union closer together without involving all the Member States.

See:

•Closer cooperation
•Pillars of the European Union 
•Social Policy Agreement