The 2016 United Kingdom European Union membership referendum took place on 23 June 2016 under the European Union Referendum Act 2015. Voters were asked whether the UK should remain a member of the European Union or leave. The result favoured leaving, prompting the UK’s withdrawal process, commonly known as Brexit.

The referendum has also been discussed in connection with allegations of Russian interference. A UK prime minister has said Russia interfered in the vote, but provided no details in the reported comments. A 2020 report by Parliament’s Intelligence and Security Committee did not reach a definitive conclusion on whether Russia had tried to influence the referendum’s result, and criticised successive governments for not fully assessing or countering the threat.