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
Accession of Montenegro to the European Union Deutsche Mark yielded, Montenegro followed suit and began using the euro as well, with no objection from the European Central Bank (ECB). The European Commission and the ECB have since voiced their discontent over Montenegro's unilateral use of the euro on several occasions.” A statement attached to their Stabilisation and Association Agreement with the EU read: "unilateral introduction of the euro was not compatible with the Treaty." The EU insists on the strict adherence to convergence criteria (such as spending at least 2 years in the ERMII system) which are not negotiable before euro adoption, but have not intervened to