Turnout for European Parliament elections has been on a downward trend ever since the first poll forty years ago.

There are many arguments put forward to explain this, including the complexity of understanding how Brussels works.

To help you get your head around this spring’s European elections, we’ve put together this handy explainer.

What is happening?

Voters across the European Union will go the polls to select the 705 MEPs to serve in the European Parliament for the next five years.

When is the vote?

As you will discover, European elections are a smorgasbord of different systems, with a distinctly disjointed approach.

It’s no different for when voters go the polls: for most, it will be Sunday, May 26; for others the 23rd, 24th or 25th.

How will Brexit affect things?

In April the EU agreed to a Brexit extension for until the end of October under the condition that the UK take part in the European elections — unless a withdrawal deal could be agreed before May 23.

How many MEPs will each country have in the parliament?

The British government has since accepted the vote will have to take place, due to a lack of time to get an exit deal ratified even if it was approved by parliament.

Prime Minister Theresa May still hopes to deliver Brexit before the summer, in which case the UK's MEPs would not take up their seats.

This would shake up how EU Parliament seats are distributed. The number of MEPs for the next five-year term would be reduced to 705, down from 751 during the 2014-2019 period.

The biggest beneficiaries would be France and Spain, who would both have five extra members in the chamber.

READ: UK will take part in EU elections, government confirms

How are MEPs elected?

Confusingly, there are different voting systems used across the EU. But all are some form of proportional representation, which is where parties gain seats in relation to the number of votes they get.

Closed lists: Some vote for parties, who have selected a fixed list of candidates to appear on the ballot paper.

The number of MEPs a party gets elected is proportional to its vote share, as long as it passes a minimum threshold, often 5%.

So if party X gets 30% of votes in a country allocated 10 MEPs, it would get 30% or 3 MEPs.

Candidates at the top of the list are chosen first.

Open lists: Other countries have more open lists where voters choose a party or indicate who is their favourite candidate.

This allows voters to change the order of the party lists and influence who is elected first, in contrast to the fixed or closed list.

Single transferable vote: There is also the single transferable vote, where electors choose as many candidates as they like and number them by preference

The numbers tell those counting to transfer the vote of any candidate that has passed the threshold to be elected or has no chance of winning.

When a winning candidate gets enough votes, all additional ballot papers with him as the first choice are ignored and second preferences counted instead.

What do MEPs do?

MEPs are elected to represent regions in some countries, like Italy, while in others, such as Germany, they have the whole country as their constituency.

They will serve a five-year term (2019-2024) and spend their time between European parliaments in Strasbourg and Brussels.

The number each country gets its proportional to its population.

Germany, the most populous, will get 96 MEPs for its 82.8 million people, while tiny Malta, with 475,000 people, has just six.

They pass EU laws and approve its budget, along with the European Council, which comprises the heads of state of each country.

MEPs represent individual countries or regions but in parliament sit in transnational groups according to political ideology.

For example, there are groupings to represent the centre-right, socialists, greens and others for eurosceptics.

MEPs also help choose the president of the European Commission, the EU’s civil service.

The largest political grouping after May’s election has the strongest mandate to have its choice head up the commission.

Last time around that was the European People’s Party, who managed to get its candidate, Jean-Claude Juncker, into the hot seat.

The process is that another body, The European Council, comprising chiefs of EU countries, first votes on a nominee chosen after taking into account the election result.

If they approve the candidate, it goes to the European Parliament, where he or she must get the support of a majority of MEPs.

Only then does he or she become president of the European Commission.

What could overshadow the election?

Firstly, growing anti-EU populism across the continent could see a louder eurosceptic voice in parliament.

This might slow down the legislative process and make decision making much more of a challenge:

Secondly, there is also the question of legitimacy: turnout at EU elections has been on a downward trend since 1979.

It’s dropped from 62% to 42% over the last four decades.

That’s despite a handful of countries, including Belgium, Greece and Bulgaria, where voting is compulsory.

READ MORE:

What does the European Parliament do?

What does the European Commission do?

What does the European Council do?