THE EUROPEAN UNION

West Germany, France and four other nations formed the European Economic Community, also known as the Common Market, in 1957, determined to banish forever the bloodshed of two world wars. The grouping became the EU in 1993 and has grown into a 28-nation bloc of more than 500 million people stretching from Ireland to the Aegean Sea, with substantial powers over member states’ laws, economies and social policies. It has its own parliament, central bank and 19 EU members use a common currency, the euro.

BRITAIN’S EXIT VOTE

Britain joined the bloc in 1973, but many Britons feel their island nation – a former imperial power with strong ties to the United States – is fundamentally different to its European neighbors. Anti-EU Britons resent everything from fishing quotas to fruit sizes being decided in Brussels.

The anti-EU view is especially strong in the Conservative Party of Prime Minister David Cameron. It was partly to appease his party that Cameron promised to hold a referendum on EU membership by the end of 2017. The prospect of Britain leaving the EU is known as “Brexit” – short for British exit.

WHAT THE POLLS SAY

The referendum’s outcome is hard to predict, because there is little precedent – Britain hasn’t had a referendum on Europe since 1975. Opinion polls were notoriously inaccurate about Britain’s 2015 election, and vary widely. Some show a lead for the “remain” side, while others put “leave” ahead.