The European Union and the United Kingdom reach agreement on the first stage of Brexit including the status of the border between the UK and Ireland.
- Twenty-three European Union countries sign a defence integration pact known as the Permanent Structured Cooperation. NATO members Denmark, Portugal and the United Kingdom (withdrawal from EU underway), and non-NATO members Malta and Ireland, opt out.
- The European Union heads of state prepare to start negotiations on a future UK-EU trade agreement in December, depending on progress with the financial "exit bill" negotiations by then.
- UK Prime Minister Theresa May announces that citizens of the European Union living in the United Kingdom will be able to acquire a "UK settled status" after the UK leaves the EU.
- European Union leaders approve negotiating guidelines that seek to secure "sufficient progress" on the rights of European Union expatriates living in the United Kingdom, on the financial terms of the separation and on a "soft border" between the Republic of Ireland and Northern Ireland, before committing to talk about a new free trade deal.
- The United Kingdom formally notifies the European Council of its intention to withdraw from the European Union and the European Atomic Energy Community. There is not yet agreement on a negotiations roadmap.