The paper examines the party system of the European Parliament (EP) between 2004–2019
through European Parliamentary Groups. It applies party system typologies in an international
case. The examined period starts from 2004, which marks the largest enlargement of the
dominating the decision-making In addition to the widely used typologies developed by Blondel
and Sartori, the present paper focuses on the relationship between the political groups in the
EP and their role in decision-making. It draws conclusions about the nature of the party system
and its changes over three cycles from the internal cohesion indices and coalition statistics of
the political groups. The party system of the EP is a polarised pluralist system dominated by
two political groups (bidominant). In the period under review, the party system of the EP can be
characterized as balanced, showing only small changes.