Nine Things To Know About This Week's Scottish Referendum

Scottish independence supporters gather outside Usher Hall ahead of the "A Night for Scotland" concert in Edinburgh, Scotland, on September 14.

On September 18, voters in Scotland will decide whether to stay in the United Kingdom or split off as an independent country. Here are nine things to know.

What are voters being asked?

A single question: "Should Scotland be an independent country?"

How did the referendum come about?

Scotland entered into political union with England in 1707 following a financially ruinous venture to set up a trading colony in Central America. Calls to shift some powers back to Edinburgh grew during the 20th century and in 1979 Scotland held its first referendum on devolution. That failed due to low turnout, but a second vote nearly 20 years later led to the setting up of the Scottish parliament with devolved powers over health, education, and local government among other areas.

After a resounding win by the separatist Scottish National Party in the 2011 Scottish elections, the U.K. and Scottish governments agreed on an independence referendum.

Who gets to vote and what are the mechanics?

Residency is key. Any British or other European Union citizen living in Scotland can vote; people born in Scotland but living outside the country cannot. Sixteen- and 17-year-olds can vote in an extension of the franchise below the U.K.’s minimum voting age of 18. There is no minimum turnout for the result to be valid. Turnout is expected to be high in any case; by the September 2 deadline, an estimated 97 percent of Scotland’s 4.4 million eligible voters had registered to cast ballots -- a record. A simple majority is required for victory.

If there's a "yes" result, when will Scotland become an independent state?

On March 24, 2016, following an 18-month negotiating period to hammer out all the details with London. The date is significant; on that day in 1603, the crowns of England and Scotland were united when King James VI of Scotland became king of England, too (as James I).

Will Scotland still have the queen?

Yes, she will remain head of state -- this referendum is about the political union of 1707, not the union of the crowns of a century earlier -- though an independent Scotland might hold another referendum on the monarchy down the line. Some experts have suggested the queen might need a governor general to act on her behalf in an independent Scotland, as is the case in other countries where she is head of state, such as Canada and Australia.

Will Scotland keep the pound?

This has been one of the key issues of the referendum. The "yes" campaign says Scotland will be able to keep the pound -- ideally in a currency union with the rest of the United Kingdom or informally through "sterlingization." But the political parties in the "no" camp have ruled out a currency union and the head of the Bank of England, Britain’s central bank, has said it is incompatible with sovereignty. The "yes" camp says that’s all a bluff, as a currency union would be in the interests of the rest of the U.K., too.

Will Scotland be in the European Union?

Likely yes, though questions remain. Independence supporters say Scotland will negotiate "from within" the EU and that in contrast to other countries that joined in recent years, all EU legislation and regulations already apply in Scotland so there would be no need for the usual lengthy accession process. But other EU countries with their own secessionist movements -- notably Spain (note: paywall) and Belgium -- might try to block Scottish accession to the EU.

What about NATO membership?

The ruling Scottish National Party (SNP), the main backer of the referendum, says it would want an independent Scotland to be part of NATO but would remove Britain's Trident nuclear weapons from the country. The head of NATO, Anders Fogh-Rasmussen, says an independent Scotland would have to reapply to join the alliance and be accepted by other members.

What happens if there's a "no" vote

The three main parties campaigning for "no" -- the Conservatives, Labour, and the Liberal Democrats -- have all promised more devolved powers for Scotland if voters reject independence. Those would give the Scottish parliament more say over tax, welfare, and spending. The knock-on effect in the rest of the U.K. could be to make voters there want more autonomy, too. Nick Clegg, the deputy prime minister, on September 12 called for devolution in England, saying some powers should be transferred to the regions.