When you send an MP from Wales to Westminster, an AM to Cardiff Bay, or your local councillor to the town hall, you know you're taking sides.
Enlargement means there will be 732 MEPs from 25 countries
Because you are well aware that the UK's political system sets a limited number of parties against each other, in a head-to-head battle for control.
But it isn't quite like that when you vote in the European parliamentary elections.
MEPs don't form any kind of government. They stay MEPs as backbench politicians, one and all.
And when MEPs arrive in Brussels, Strasbourg or Luxembourg, they have to seek alliances beyond normal party boundaries.
As a general rule, MEPs sit in large political groups which cross international boundaries, rather than in separate national political blocks. Until the run-up to next month's elections, there have been seven of these groups in the European Parliament, with none having overall control.
The EU Parliament's corridors of power run differently
The new enlarged parliament will have 732 MEPs, which means that the target for any group to achieve overall control will be 367. Given the current balance of power, then this would require a significant swing towards the right.
So if MEPs can't take part in government, then what do they actually do?
They scrutinise the European Commission, and share some responsibilities for introducing new laws right across the EU.
Some Euro laws since 1999
Improving bathing water standards
Seatbelts for children
Maximum working hours for junior GPs and lorry drivers
Ban on animal testing for cosmetics
GM food labelling and product restrictions
They also keep a close watch on the EU's budget and spending, as well as develop their own policy agendas.
What that effectively means is that MEPs, and decisions they help to make at the European Parliament, have a direct impact on lives in Wales.
Welsh MEPs earn the same as UK MPs: £56,358 in 2003.
The budget for the European Parliament in 2004 is 1,231 m euros (£821.5m) This covers staff costs, buildings, MEPs' travel allowances and expenses, and includes the costs of translating documents into the EU's official languages.
It also includes the cost of moving MEPs and staff between Brussels and Strasbourg. That works out at about 2.5 euros for each inhabitant of the enlarged EU.