There were three political institutions which held the executive and legislative power of the EEC (the Council, the Parliament and the Commission) plus one judicial institution (Court of Justice) and a fifth body (Court of Auditors). These institutions (except for the auditors) were created in 1957 by the EEC but from 1967 they applied to all three Communities thank to the Merger Treaty which also gave the Council and Commission of the EEC responsibility over ECSC and EAEC affairs.
These governed the three Communities till the establishment of the European Union in 1993, when the Maastricht Treaty was signed and because of it, these institutions became those of the European Union, though limited in some areas due to the pillar structure.
European Communities 