The Conservatives traditionally lean to the political right; Labour has its origins in the trade union movement, and leans left.
Those two titans are joined by the centrist Liberal Democrats, a once-strong party almost wiped out in the last election; the environmentally-aware Greens; and the pro-Brexit right-wing UK Independence Party (UKIP).
England accounts for 533 of the seats - it's got the biggest population in the UK by far.
In Scotland, the Scottish National Party (SNP) holds 56 of 59 seats - a dominant position it won in 2015 at Labour's expense. The nationalists want to hold on to that. Internationally, they're best known for campaigning for Scottish independence.
In Wales, Plaid Cymru - a Welsh term meaning the Party of Wales, and pronounced "PLIGHD KUM-ri"- has just three seats out of 40. And Northern Ireland accounts for another 18 seats.
A tale of two leaders
The UK voting system for general elections is simple - whoever gets the most votes in their constituency wins the seat. No transfers, and no proportional representation.
That system tends to favour the big established parties over the smaller ones, and tactical voting is a big part of the process.
All of which means there's a sharp focus on not just the local candidates, but the party leaders who could be the prime minister.
Those leaders are Theresa May (Conservatives) and Jeremy Corbyn (Labour).
Recent polls have given The Conservatives a lead of anywhere between one and 12 points - and they are still widely seen as the most likely to win this election.
But if they end up losing seats in parliament, it's possible - if unlikely - that someone with completely different plans could be sitting at the negotiating table in Europe.
Then again, Labour says it will still push ahead with Brexit - so it's a question of how rather than if.
There's another possibility - one recent poll, splashed on the front page of the Times newspaper suggested the Tories could lose seats, resulting in a "hung parliament".
That's just a British term for no single party having an outright majority. That might be common in many nations that usually have coalition governments, but it's a little rarer in the UK.
I'm a foreigner who lives (or wants to live) in the UK. Might this affect me?
Almost certainly. Immigration is a big issue on the campaign trail.
The current Conservative government wants to reduce net migration - the difference between people entering the UK and people leaving - to "tens of thousands" a year (it's currently about +248,000 a year).
The Conservatives' manifesto says they want to double the Immigration Skills Charge - a levy of up to £1,000 ($1,300) they introduced in April, charging companies for every foreign worker they sponsor.
They've promised to increase the minimum income someone has to earn to come on a family visa, and "toughen" visa requirements for students.
And the party says it will triple the Immigration Health Surcharge - a levy foreigners have to pay to let them use the National Health Service (NHS) - from £200 to £600.
Labour acknowledges that Brexit means the free movement of people from Europe will end - but promises it won't "scapegoat migrants".
Instead of raising income thresholds for migrants, Labour plans to end them - but oblige people coming here to survive without falling back on public money. Its manifesto contains a pledge to "protect those already working here, whatever their ethnicity" and says it won't count international students in the main immigration numbers.
But at the same time, it says it will recruit an extra 500 border guards.
Both the Liberal Democrats and the Green party support free movement between the UK and the EU. The Lib Dems say they would allow "high-skilled immigration", and, like Labour and Plaid Cymru, take students out of the immigration statistics.
The Greens also say their immigration and asylum system would be "humane". And Plaid Cymru says it will introduce a new, Wales-specific visa.