The Baltic countries of Estonia, Latvia and Lithuania have opened their borders to one another, creating a coronavirus "travel bubble".
Anybody arriving from outside the zone however must self-isolate for 14 days.
This is the first "travel bubble" in Europe since nations began shutting their borders earlier this year in response to the coronavirus outbreak.
European Union officials are now trying to encourage other countries to end restrictions on movement as concerns grow about the economic impact of the lockdown. The Baltic states expect their economies to shrink by up to 8% this year.
Under the new rules, anyone who has not travelled outside the Baltic states in the past two weeks, is not infected, and has not been in contact with somebody who has tested positive may travel freely to the other nations.
The sparsely populated Baltic states have not been as badly affected by the pandemic as some of their European neighbours.
Germany has begun to partially reopen, and has said it plans to open all its borders on 15 June provided the new case number does not worsen.