The Treaty on European Union, also known as the Maastricht Treaty, entered into force on 1 November 1993, following the ratification of the Treaty by all twelve Member States of the European Communities. As a result, what used to be known as the European Community (EC) has become known, through common usage, as the European Union (EU).

The European Community of course continues to exist as the first and most important foundation of the European Union. Therefore, the expressions, the EC, European Community, will continue to be used especially in certain documents of a legal character such as official acts adopted on the basis of the Treaty establishing the European Community.

The role and responsibilities of the European Union, however, is not limited to the EC (including the stages for achieving the economic and monetary union, the European Coal and Steel Community and Euratom (the European Atomic Energy Community) but also applies to new areas under the Maastricht Treaty such as the Common Foreign And Security Policy and cooperation in the field of Justice And Home Affairs.

The Union as a whole is served by a single institutional framework. The former EC Council of Ministers is now called the Council of the European Union or EU Council. The European Parliament and the European Court of Justice have maintained their original names as has the Commission of the European Communities but which can be called European Commission in short.

In a similar way, the use of the European Union or EU is recommended to call the territory formerly commonly referred to as the EC in such expressions as: The EU Member States, EU population, EU market or industry, etc.