Citizens in the 28 European Union nations will go to the polls this week in an atmosphere of uncertainty — with the specter of Brexit looming over the process and a growing nationalist, euroskeptic movement drawing voter support — to cast ballots for the bloc’s only directly elected body: the European Parliament.

The European Union is complex by design, a fact that can perplex voters and vote-watchers alike, often resulting in a low turnout.

But this time is different. Nationalists have gained ground across Europe, and as they head into the elections with a newly united front, the vote is being seen as the latest test of their influence. Polls suggest that populist parties could be positioned to make big gains.

Here’s a guide to the European Parliament elections, a notoriously confusing system made even more so by changing dynamics within the bloc.

How does the European Parliament work?

Voters will elect the 751 members of the European Parliament to five-year terms, with the number of seats for each nation determined primarily by its population.

Each country uses a slightly different process, with the uniting requirement that the number of seats won by political parties be roughly proportional to their share of the vote. Member nations must hold their elections no earlier than Thursday and no later than Sunday.

The system is relatively new — the first elections were held just 40 years ago — and it is still evolving. Read more via New York Times