MEPs in Parliament are organised into seven different parliamentary groups, including thirty non-attached members known as non-inscrits. The two largest groups are the European People's Party (EPP) and the Socialists & Democrats (S&D). These two groups have dominated the Parliament for much of its life, continuously holding between 50 and 70 percent of the seats between them. No single group has ever held a majority in Parliament.[70] As a result of being broad alliances of national parties, European group parties are very decentralised and hence have more in common with parties in federal states like Germany or the United States than unitary states like the majority of the EU states.[46] Nevertheless, the European groups were actually more cohesive than their US counterparts between 2004 and 2009.[71][72]
Groups are often based on a single European political party such as the socialist group (before 2009). However, they can, like the liberal group, include more than one European party as well as national parties and independents.[73] For a group to be recognised, it needs 25 MEPs from seven different countries.[74] Once recognised, groups receive financial subsidies from the parliament and guaranteed seats on committees, creating an incentive for the formation of groups. However, some controversy occurred with the establishment of the short-lived Identity, Tradition, Sovereignty (ITS) due to its ideology; the members of the group were far-right, so there were concerns about public funds going towards such a group.[75] There were attempts to change the rules to block the formation of ITS, but they never came to fruition. The group was, however, blocked from gaining leading positions on committees — traditionally (by agreement, not a rule) shared among all parties.[76] When this group engaged in infighting, leading to the withdrawal of some members, its size fell below the threshold for recognition causing its collapse.[77]