COSAC, the Conference of Parliamentary Committees for Union Affairs of Parliaments of the European Union, established in Madrid in 1989, is a forum for cooperation, exchange of information and best practice between parliaments of the European Union, in particular with regard to the practical aspects of parliamentary scrutiny of Union affairs. It is the only forum for interparliamentary cooperation in the European Union regulated by the Treaties. The functioning of COSAC is organised by its rules of procedure, currently applicable in the version adopted in 2011 in Budapest.

COSAC plenary meetings take place twice a year in a member state currently holding the Presidency of the Council of the EU. They are prepared at the meeting of the Chairpersons of the Committees for Union Affairs and of the representatives of the European Parliament, held before each plenary sitting, in agreement with the Presidential troika of COSAC (delegations of national parliaments of the current, preceding and following Presidency, and the European Parliament). Each delegation consists of two members of its parliament.