Prior to 1 May 2004 the European Union had fifteen members. On that date ten new member states were admitted. This article describes the party affiliations of the leaders of each member-state represented in the European Council from the beginning of 2004 until 1 May. The list below gives the political party that each head of government, or head of state, belonged to at the national level, as well as the European political alliance to which that national party belonged. The states are listed from most to least populous. More populous states have greater influence in the council, in accordance with the system of Qualified Majority Voting.

During the period in question only two changes of government occurred: in Greece and Spain, and taken together these left the overall balance of party affiliations in the Council unchanged.

• Presidency of the Council of the European Union

• Council of the European Union (official website)