Trying to figure out what each of the main European Union institutions does is not easy.

As EU citizens vote in four days of elections -- with most balloting happening Sunday -- we look at the bodies based in Brussels and elsewhere.

- European Commission -

The European Commission is the EU's executive arm. It is the only institution that can propose EU laws.

The commission is responsible for enforcing EU law and represents the bloc in trade negotiations on behalf of member countries, which constitute a single market.

The commission is also the EU's powerful antitrust regulator, with power to probe violations and impose hefty fines. The size and wealth of the bloc means EU competition laws influence other jurisdictions around the world in what is called the "Brussels effect".

Around 32,000 people work for the commission, which is led by a president. All the EU commissioners, including the president, are collectively known as "the college" rather than the cabinet. Customarily there are as many commissioners as there are member states, with one from each.

Under EU treaty law, the president is chosen by the bloc's leaders, "taking into account" the results of the European Parliament elections.

The parliament -- which argues the commission president should come from the political grouping receiving the most votes -- needs to approve the leaders' choice via a simple majority.

The current president is German conservative Ursula von der Leyen, from the leading European People's Party. She is seeking a second five-year mandate.

There is also a "high representative" who coordinates foreign policy with member states. The role is currently held by Josep Borrell.

- European Parliament -

The parliament is the only EU institution directly elected by European citizens. It also has a five-year mandate, though its president -- in effect, speaker -- has a two-and-a-half-year term.

There will be 720 lawmakers in the next parliament, compared with 705 in the outgoing one, to reflect demographic growth in the EU.

The members of the European Parliament (MEPs) are responsible for adopting laws on a vast array of subjects, including trade deals, energy, the environment, migration and the bloc's budget, among others.

Lawmakers negotiate the texts with member states, represented by the Council of the EU, before final adoption. The commission also takes part in the discussions.

The parliament's official seat is in Strasbourg, France, where week-long plenary sessions are held nearly every month. But day-to-day work goes on in Brussels.

- European Council -

The European Council is made up of the EU heads of state and government.

Leaders usually meet in Brussels four times a year for summits that frequently end in the early hours of the morning after drawn-out discussions. In exceptional cases they can go on for days.

The leaders together shape the bloc's policy aims, handle politically sensitive issues and strike agreements on topics where their ministers were unable to reach an accord.

The council's significance has grown as the EU has faced crisis after crisis, including the coronavirus pandemic and Russia's 2022 full-scale invasion of Ukraine.

- Council of the EU -

Not to be confused with the human rights watchdog the Council of Europe -- a pan-European body not part of the EU despite sharing the same flag -- the Council of the EU is the name given to EU ministers grouped together by portfolio.

For example, the EU's 27 finance or agriculture or environment ministers gather for regular meetings, usually in Brussels but sometimes in Luxembourg. Each of those meetings is known as a Council of the EU meeting.

Each EU country takes turns holding the six-month rotating presidency of the bloc to chair the ministers' meetings.

The Council of the EU gives the green light to laws, usually by qualified majority -- which means at least 15 out of 27 EU nations must be in favour, as long as they account for at least 65 percent of the bloc's population.

Foreign policy or taxation issues can only be adopted unanimously, giving each member state power of veto.

- Other bodies -

Navigating the acronymic alphabet soup for other EU bodies is no easy feat.

There is the European Court of Justice (ECJ), the European Central Bank (ECB) and the European Medicines Agency (EMA).

There are many bodies to enforce EU rules such as the European Data Protection Board (EDPB) and the Italy-based European Food Safety Authority (EFSA).

And there's also the Fundamental Rights Agency (FRA), the European Public Prosecutor's Office (EPPO) and the European Anti-Fraud Office (OLAF).