The vast majority of MEPs belong to one or other of the political groups. Members who do not belong to any of the groups are known as 'non-attached Members'. A political group must include MEPs from more than one member state and have a minimum number of members.

There are currently 7 political groups in the Parliament, drawing on more than a hundred national parties. Several of the political groups have links to parties at European level, recognised by the Treaty as 'a factor for integration within the European Union which contributes to forming a European awareness and to expressing the political will of the citizens.'

Each political group has a president (or in the case of the Green/EFA Group, two co-presidents, one woman and one man), a bureau and a secretariat.

Before votes in plenary sessions, the groups consider reports from Parliament's committees in the light of their political view and often table amendments to them. They also play an important part in deciding on the agendas for plenary sessions and choosing the topical issues to be placed on these agendas.

Being part of a political group is important for MEPs, as it means that work can be shared out between MEPs (no one MEP could ever follow the 100s of legislative proposals that pass through Parliament each year!), as well as financial resources. By pooling resources, MEPs have access to a number of specialist advisers hired by the group to cover each subject area.