The EU's digital COVID passports came into use on Thursday (July 1).
They are meant to enable travel for people who can show they've been fully vaccinated, have immunity due to recent infection, or can show a negative virus test result.
The certificates take the form of a QR code that can be printed out or shown on a phone.
At Paris's Orly Airport, some of the first passengers to try out the system seemed happy.
It's easy to use says this man.
Airports are worried though.
They have warned of long queues if countries don't do more to coordinate the rollout.
That as EU member states take different approaches to handling the system.
But at Orly on Thursday, Air France staff said the codes were speeding up checks.
Laurent Millet is the airline's station manager at one terminal:
"The QR code is standardized across the EU countries, and it's useful for the health restrictions towards European countries. For example, if someone decides to spend their holidays in several countries and if they are vaccinated, they can use that one QR code to go to the different European destinations planned in their journey."
EU member states can hit an 'emergency brake' to bar travelers from regions where there is a spike in virus cases.
Germany is already limiting arrivals from Portugal on such grounds.
Even so, the travel industry will be banking on the scheme to get Europe moving again this summer.