The member states of the European Union speak with the same voice on many issues. The EU is the world's largest economic union, Customs Union and donor of humanitarian and development assistance, and thus has an extensive network of delegations around the world mainly operating in the framework of External Relations, for which the European Commission is the main decision body. The EU also represents shared political and security viewpoints held by its member states, as articulated in the Common Foreign and Security Policy.
The EU's predecessor, the European Coal and Steel Community, opened its first mission in London in 1955, three years after non-EU countries began to accredit their missions in Brussels to the Community. The US had been a fervent supporter of the ECSC's efforts from the beginning, and Secretary of State Dean Acheson sent Jean Monnet a dispatch in the name of President Truman confirming full US diplomatic recognition of the ECSC. A US ambassador to the ECSC was accredited soon thereafter, and he headed the second overseas mission to establish diplomatic relations with the Community institutions.
The number of delegates began to rise in the 1960s following the merging of the executive institutions of the three European Communities into a single Commission. Until recently some states had reservations accepting that EU delegations held the full status of a diplomatic mission. Article 20 of the Maastricht Treaty requires the Delegations and the Member States’ diplomatic missions to "co-operate in ensuring that the common positions and joint actions adopted by the Council are complied with and implemented".
Management of the EU External Relations is conducted by the European External Action Service which reports to the High Representative for Foreign Affairs. Delegates are generally sent only to capital cities and cities hosting multilateral bodies.
The EU missions work separately from the work of the missions of its member states, however in some circumstances it may share resources and facilities. In Abuja, the EU mission shares its premises with a number of member states. The European Commission also maintains representation in each of the member states. For details on diplomatic representation, see Foreign relations of the European Union#Diplomatic representation.