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 EU regulated by the Treaties. The functioning of COSAC is organised by its rules of procedure, currently applicable in its version adopted in 2011 in Budapest.

COSAC plenary meetings take place twice a year in the member state holding the Presidency of the Council of the EU. Each national parliament is represented by a maximum of six members of its Committee(s) for Union Affairs, while the European Parliament is represented by six MEPs. Representatives of parliaments of the candidate countries, representatives of the EU institutions and special guests are also invited to the meetings as observers. In a given semester, the Committees (or the Committee) for Union Affairs of the Presidency parliament hold(s) the Presidency of COSAC and its meetings are chaired by the Chairperson(s) of the Committee(s).