Should Britain stay in the European Union or leave?

That’s the question facing Britons, who are being asked to vote on a potential “Brexit” from the EU, the economic and political union that allows goods and people to move across its 28 member states as if they were one country. Critics of Britain’s membership in the bloc say it chips away at the country’s sovereignty and takes more than it gives back. Supporters argue EU membership strengthens Britain.

On Monday, Prime Minister David Cameron told lawmakers why he thinks Britain should remain in the European Union, just days after he secured concessions from his fellow European leaders over the U.K.’s membership in the bloc.

Britain can have best of both worlds,” he said. He described leaving the EU as a “leap into the dark.”

When do Britons decide?

On June 23, Britons will vote in a referendum that asks the following question: “Should the United Kingdom remain a member of the European Union or leave the European Union?”

British, Irish, and citizens from the Commonwealth who are over 18 and who live in the U.K. can vote, as can U.K. nationals who have lived outside the country for less than 15 years. Their answer—a simple “yes” or “no”—will determine not only Britain’s future in the bloc, but also that of post-war Europe’s most ambitious experiment.

Why is a referendum being held in the first place?

At the heart of the debate in Britain is the question: Does EU membership benefit the U.K.? Britons voted in a referendum in 1975 on whether to stay in what was then called the European Economic Community (EEC). But the bloc has evolved since then: It has grown from 12 member states in the EEC to 28, has its own currency, and its decisions have a wider impact across the bloc now than at any time in the past. Critics of the EU want Briton to have a say once again on whether to be part of the bloc because, they say, the EU is eroding Britain’s sovereignty, and hurts British businesses because of its onerous regulations. In 2013, Cameron backed their demand for a referendum.  

What are the issues at play?

Cameron had sought changes in four areas of Britain’s membership of the EU: economic governance, competitiveness, sovereignty, and immigration. He’s received concessions—in varying amounts—in all those areas. Among those major concessions, which were announced last week following a meeting with European leaders, Britain “is not committed to further political integration into the European Union”; can limit benefit payments to workers from other EU countries (in-work benefits) for four years; and will not be disadvantaged because it has not adopted the euro, the common EU currency that is used by 19 of the bloc’s 28 members.

For a full assessment of each of Cameron’s demands to the EU—and how he fared—go here.

Do these concessions satisfy skeptics of EU membership?

Probably not. But we’ve known for some time that the country is evenly divided on the issue of EU membership—as is evinced by divisions within Cameron’s own Cabinet. Six Cabinet ministers will campaign for Britain to leave the EU, and Boris Johnson, the London mayor, has said Britain’s continued presence in the EU would lead to an “erosion of democracy.” But supporters of membership, including Defense Secretary Michael Fallon, said the country would be taking a big gamble” with its security if it votes to leave. Supporters of continued membership believe the EU is a boon to the United Kingdom. It makes trade easier; provides young, cheaper workers from other European countries; and makes the country more secure. Cameron’s position on membership is also supported by some of Britain’s biggest companies.

The Labour Party, the main opposition; the Scottish National Party, which governs Scotland; Plaid Cymru, the Welsh party; and Liberal Democrats are campaigning to stay in. The Conservatives say they will remain neutral. The U.K. Independence Party, which is deeply skeptical of the EU, will campaign to leave.

What does Europe think of all this?

European leaders presumably want Britain to stay because they have negotiated with Cameron to give him many of the things he wants, including special exceptions currently not enjoyed by many other members. European lawmakers fear a “Brexit” would threaten the EU itself, causing the bloc that has been buffeted since 2008 by crises of economy, security, and migration to breakup. And Europe’s citizens want Britain to stay—by a fairly wide margin. We’ll know if Britons share that view in four months.