Britain voted to leave the European Union almost three years ago. But, so far, it is still an E.U. member. Despite the Brexit vote in June 2016, the country has not Brexited.

With British Prime Minister Theresa May in Brussels on Wednesday for an emergency summit to plead for a second extension to her Brexit deadline, we thought it was worth taking another look at how we got here and what the big questions surrounding Britain’s path out of the E.U. have been.

So, let’s start with the most basic:

Q: What is Brexit?

A: May has said, “Brexit means Brexit.” But what that means is that Britain plans to leave the E.U., gaining the ability to control its borders and make its own trade deals — or, as some people see at it, losing the automatic free-movement and free-trade rights that come with membership in the bloc.

Q: Why is Britain leaving the E. U.?

A: Basically, because Brits voted for it, 52 to 48 percent, in a referendum on June 23, 2016. Concerns about immigration and sovereignty were the top reasons people voted to leave.

Q: Who voted for Brexit?

A: England and Wales voted to leave, while Scotland and Northern Ireland wanted to remain. London was strongly against. The vote divided both main political parties: Conservatives and Labour. Labour leader Jeremy Corbyn voted to remain, though he is lukewarm on the E.U. and has regularly criticized it as a capitalist club. May, a Conservative, also voted to remain — though she asserts, repeatedly, that she is committed to delivering on the referendum result. Among the most notable Brexiteers are Boris Johnson, May’s former foreign secretary, and Jacob Rees-Mogg, another Conservative.

Q: So when does Brexit happen?

A: The original departure date was supposed to be March 29. But Parliament hasn’t yet agreed on how to leave. It has rejected May’s withdrawal plan three times. Last week, E.U. leaders granted a short extension. If British lawmakers had approved May’s deal this week, they would have left the E.U. by May 22. Now, in theory, they must plan an alternative by April 12 or leave without any transition provisions or protections that evening.

But May has traveled to Brussels this week for an emergency summit with leaders, in the hope of getting an extension.

British Prime Minister Theresa May spoke to reporters after arriving in Brussels April 10 for a summit focused on Britain's exit from the European Union. (Reuters)

Q: Why does Parliament need to approve Brexit, after there was already a referendum?

A: The referendum wasn’t legally binding, and it asked people only whether they wanted in or out of the E.U. — not how they should leave. Because Britain is a parliamentary democracy, meaning Parliament is sovereign, it was agreed after a lengthy legal debate that Parliament would get a “meaningful vote” on the deal — a decision that significantly complicated May’s negotiations.

Q: Why does May want another extension?

A: To put it simply, there’s not really another option. May’s deal has been rejected multiple times, and attempts to find an alternative have foundered. That only leaves one option: a “no deal” Brexit that could be disastrous for the British economy.

Q: Will Europe agree to this?

A: There is, understandably, a little concern among European nations about this seemingly never-ending process. An extension would raise some real practical issues, too, including the farcical development of Britain having to field candidates for European Parliament elections next month.

But European leaders aren’t keen on a “no deal” Brexit either, so it’s expected that there would be some sort of extension. It just depends how long that extension would be.

Q: How long could an extension be?

A: There’s a divide between two ideas: a short delay and a long delay. A short delay would be designed to give May more time to get some kind of Brexit deal through Parliament. This might be just a few weeks or a month or two.

The alternative would be a long delay designed to calm things down and ramp down some of the pressure. Some E.U. policymakers have argued for a “flextension” that would set a date for Britain’s E.U. exit far in the future but allow Britain to leave as soon as it comes up with a viable plan.

Q: What was in May’s thrice-rejected withdrawal deal?

A: The 585-page deal laid out things such as a timetable for a transition period, what happens to E.U. nationals living in Britain and the amount of money Britain has to pay the E.U. It doesn’t get into anything about trade deals or other aspects of the future relationship between Britain and the E.U. That’s saved for a separate set of negotiations, to the chagrin of all those with Brexit fatigue.

The Washington Post's Michael Birnbaum explains what British Prime Minister Theresa May is seeking ahead of an April 10 European Union leaders summit. (Sarah Parnass, Quentin Aries/The Washington Post)

Q: Why don’t people like May’s deal?

A: Hardcore Brexiteers think she made too many concessions to Europe. They want a more decisive split. Those who are more pro-Europe argue that the deal risks economic damage to Britain without sufficient benefits.

Q: What’s the issue with the Irish border?

A: An open border on the island of Ireland has helped to resolve decades of conflict — allowing “unionists” in Northern Ireland to feel securely part of Britain while “republicans” in the north can feel connected to the Republic of Ireland in the south. But that open border has been possible only because the E.U.’s customs union and single market avoid the need for border checks. Once Northern Ireland leaves the E.U., along with the rest of Britain, there will have to be a different way to preserve an open border and maintain peace. That’s where the backstop comes in.

Q: What’s the backstop?

A: It’s an insurance policy to guarantee an open border between Ireland and Northern Ireland. Until a future trade deal somehow dispenses with the need for border checks, or until technology is developed that does the job of border agents and achieves an invisible border, the backstop would require Britain to remain in the E.U. customs union and parts of the single market. That’s controversial in part because Britain would be subject to E.U. rules even after losing its say over them.

Q: Could Brexit be stopped?

A: Theoretically, yes. The E.U.’s highest court ruled last year that Britain could unilaterally reverse its decision to leave. A petition to cancel Brexit has garnered more than 5 million signatures, becoming the most popular petition hosted on Parliament’s website. Those numbers triggered a parliamentary debate for April 1. But many lawmakers would be wary of supporting a complete reversal, and, anyway, they’re several steps away from that happening.

Q: Couldn’t Britain just hold a second referendum?

A: Since the Brexit vote in 2016, the prospect of a second referendum has gone from something barely imaginable to something remotely possible. The idea has considerable public support. About a million people demonstrated in London in favor of a “people’s vote” on March 23. But critics argue that a second referendum would be deeply damaging to democracy and a betrayal of those who voted in 2016 to leave. It could also unleash further political chaos.

Q: Have people changed their minds on Brexit?

A: Certainly some have. But many people feel even more strongly now about the stance they took and have begun to define themselves as leavers or remainers. Polls suggest a slight majority of Britons would now opt to remain in the E.U., but that swing is partly the result of changing demographics. Younger people are overwhelmingly pro-remain, and teens who couldn’t vote in 2016 are now of voting age. Meanwhile, the majority of voters 65 and older voted to leave — and some of them have since died.

Thousands of people protested in central London March 23 to demand a second referendum on Brexit. Organizers said more than 1 million people assisted the march. (Amber Ferguson, Karla Adam/The Washington Post)

Q: What’s the worst-case scenario for Brexit?

A: Most economists would say a “no-deal Brexit,” a scenario in which Britain leaves without an agreement with the E.U. and without the two-year transition period that comes with it. Most probably, Britain would revert to World Trade Organization trade rules at its borders. But the sudden break could cause major disruptions to trade and travel. The International Monetary Fund projected that up to 8 percent of Britain’s gross domestic product could be lost.

Q: Yikes. Are people prepared for that?

A: Britain and other E.U. countries have put together elaborate and costly contingency plans. Brits have also been hoarding toilet paper and chocolate just in case.

Q: How likely is a no-deal Brexit?

A: It’s definitely possible. One study that came out before May made her deal last year estimated there were five possible scenarios for Brexit. All but one resulted in no deal.

Q: Does the E.U. want a no-deal for Britain?

A: European leaders have voiced real concerns about a no-deal Brexit. It could disrupt their own agreements, too. But the E.U. is also worried about other countries trying to leave the bloc, so it is driving a hard bargain with Britain and offering few concessions.

Q: Have E.U. leaders tried to help May at all?

A: To a degree, yes. In a letter published Jan. 14, European Council President Donald Tusk and European Commission President Jean-Claude Juncker explained they did not want the Irish backstop to come into force, describing it as a “suboptimal trading arrangement for both sides.”

However, they also said there was little room for more negotiations, writing: “We are not in a position to agree to anything that changes or is inconsistent with the Withdrawal Agreement.” After the deal was voted down a second time, E.U. chief negotiator Michel Barnier basically said the E.U. had done what it could do.

Q: Do any British politicians have a better idea?

A: Others claim to. Corbyn says he could solve the Irish border problem without a backstop, for example, and avoid a no-deal Brexit. May and Corbyn are trying to work together to come up with an idea, but opposition leaders have complained that May has not moved far from her red lines.

So, we probably won’t find out how these ideas work in practice unless May loses her job.

Q: What would happen then?

A: ‾\_(ツ)_/‾

Q: I have more questions that were not answered here.

A: We all do. Send them to us, and we’ll try to answer them in an update.

Karla Adam and William Booth in London and Marisa Bellack, Emily Tamkin and Siobhán O’Grady in Washington contributed to this report.