Institutional seats of the European Union are based in Luxembourg City along with the European Investment Bank. The Economic and Social Committee and the Committee of the Regions are entirely based in Brussels while the European Central Bank is based in Frankfurt and Europol is the only agency to have its seat fixed by the treaties, in The Hague. Separately, the Treaty of Nice establishes Brussels as the venue for all formal summits of the European Council after 2004. However some extraordinary sessions are sometimes held outside the city. The European Council's seat is however fixed by a declaration rather than a protocol, meaning it is
European Central Bank examples where the ECB is less transparent than other institutions: In return to its high degree of independence and discretion, the ECB is accountable to the European Parliament (and to a lesser extent to the European Court of Auditors, the European Ombudsman and the Court of Justice of the EU (CJEU). Although no interinstitutional agreement exists between the European Parliament and the ECB to regulate the ECB's accountability framework, it as been inspired by a resolution of the European Parliament adopted in 1998 which was then informally agreed with the ECB and incorporated into the Parliament's rule of procedure. The