The apportionment of seats within the European Parliament to each member state of the European Union is set out by the EU treaties. According to European Union treaties, the distribution of seats is "degressively proportional" to the population of the member states, with negotiations and agreements between member states playing a role. Thus the allocation of seats is not strictly proportional to the size of a state's population, nor does it reflect any other automatically triggered or fixed mathematical formula. The process can be compared to the composition of the electoral college used to elect the President of the United States of America in that, pro rata, the smaller state received more places in the electoral college than the more populous states.

The European Parliament (EP) is one of the legislative bodies of the European Union and one of its seven institutions. Together with the Council of the European Union, it adopts European legislation, following a proposal by the European Commission. The Parliament is composed of 705 members (MEPs), due to rise to 720 after the June 2024 European elections. It represents the second-largest democratic electorate in the world, with an electorate of 375 million eligible voters in 2009.