After more than a year of relative inactivity, it looks like U.S. air travel to Europe is starting to make its comeback—as evidenced by the fact that major U.S. carriers Delta and United Airlines are adding summer service to those European countries that are opening their borders to fully vaccinated or COVID-19 tested-negative Americans.

The Continent is collectively doing its best to ensure that its travel sector can safely allow for foreign visitors when the 2021 summer season arrives. The European Union (E.U.) is already developing a shared digital vaccination certification to help facilitate cross-border travel within the 27-block, though this has yet to be released.

European Commission President Ursula von der Leyen has also indicated she anticipates that fully vaccinated U.S. tourists will be welcomed in the E.U. sometime this summer. Certain E.U. members that are more dependent on foreign tourism markets to support their economies, like Greece, Italy, Portugal, Spain and Croatia, are especially eager to bring back visitors.

With countries like Greece and France set to start lifting travel bans this month, it’s looking likely that Transatlantic flights will soon resume on an even larger scale. In fact, a new smarTours survey discovered that Europe is Americans’ most-desired destination for 2021.

And, though the post-Brexit United Kingdom (U.K.) won’t align its own policies with E.U. regulations, it has lately established a roadmap for reopening to international travel, starting May 17. As things currently stand, U.S. travelers would need to fulfill pre- and post-travel testing requirements, plus complete a 10-day quarantine, in order to visit the U.K.

New Routes:

According to Business Insider , Delta Air Lines is set to debut new service between New York and Croatia, which opened to Americans in April, starting July 2. This will be Delta’s first-ever nonstop route to the Southeast European country. Service will consist of four-times-weekly departures from New York’s JFK Airport to Dubrovnik Airport (DBV), with return flights on Tuesdays, Thursdays, Fridays and Saturdays.

United Airlines will launch its own service to Croatia on July 8, running thrice-weekly flights between Newark Liberty International Airport and Dubrovnik. Departures will run on Mondays, Thursdays and Saturdays, with return flights on Sundays, Tuesdays and Fridays.

Both Delta and United are also introducing routes to the other two prominent European nations welcoming American travelers: Iceland , which reopened to fully vaccinated foreign visitors on March 18; and Greece , opening to vaccinated or tested PCR-negative travelers on May 15.

United will start flying to Reykjavik, Iceland from Newark on June 3 and Chicago on July 1. Delta currently flies from New York to Reykjavik, and will also begin serving the Icelandic capital city from Boston on May 20 and Minneapolis on May 27.

United is set to resume its routes from Newark to Athens on June 3 and start flying from Washington, D.C. to Athens on July 1. Delta will resume its route from New York to Athens on May 28 and initiate a new route between Atlanta and Athens on July 2.