One of the major challenge of the European Community is to adapt an initial institutional system to a newsituation. European Union’s enlargement created a new context in its architecture and, also, in solving new andspecific problems requested by this enlargement. The institutions became over-numbered and not enough optimal intheir decisions. Also, different new members of the Community had different visions about the future of EuropeanUnion, about the institutional system, about the major objectives of the Union, etc. This article focuses on some ofthese preoccupations and some solutions that should be able to find to these challenges. The most important EU’sinstitutions were reorganized and improved by the most important European Treaties, and new directions weredrawn in the way of creating the most representative and efficient institutional system.