The position of UK Citizens living in the EU will depend on whether or not the UK and the EU27 successfully conclude a Withdrawal Agreement, either before 29 March 2018 or at some time afterwards.
If the UK concludes the proposed Withdrawal Agreement, or something close to it, there will be a transition period in which all existing rights of citizens will remain as they currently are under the UK's EU membership until 31 December 2020. After that the rights of citizens will be determined by the content of that agreement and any other subsequent international agreements made between the UK and the EU.
If the UK does not conclude a Withdrawal Agreement with the EU27 prior to leaving the European Union the rights of EU citizens in the UK will be subject to the decisions of the UK Government. Citizens of the UK living in the EU will become 'third country citizens' and their rights will be dependent on the host member state. Under the EU treaties the rights of third country citizens are a matter for the member states.
These pages cover the general advice that is available to citizens in these circumstances. Some is more complete than others. Content in these pages is accurate at the time of publication but may be subject to change. Please check against the cited sources.