If you're an EU, EEA, or Swiss citizen you must apply to the EU Settlement Scheme to ensure that you can continue to live in the UK after 30th June 2021 in the event of the UK leaving the EU.
If your application is successful, you’ll get either settled or pre-settled status, depending on your circumstances. The EEA includes the EU countries and also Iceland, Liechtenstein and Norway.
Settled and pre-settled status for EU citizens and their families enables EU citizens to protect the rights they currently have in the UK. Applicants will only need to prove their identity, demonstrate their UK residence, and declare any criminal convictions.
The deadline for applyng is 30th June 2021 however if the UK leaves without a deal, the deadline for applying will be 31st December 2020 and you will need to be living in the UK before it leaves the EU to apply.
You find out further informationon the Governments website here: https://www.gov.uk/settled-status-eu-citizens-families