Travelers using Southwest Airlines can book flights to Europe thanks to a deal with Icelandair. And, for now at least, all of Southwest’s partner flights to Europe will run through Baltimore.

Under a partnership that went into effect Thursday, connections to Iceland and points beyond in Europe are available from Baltimore through Icelandair.

Southwest Airlines is the biggest carrier at Baltimore-Washington International Thurgood Marshall Airport, accounting for just under 80% of travelers. Icelandair operates one daily round-trip flight between BWI and Iceland, an airport spokesperson said.

“This is an important, positive air service development for BWI Thurgood Marshall Airport. BWI Marshall is a key gateway for Southwest, and the airline’s largest operation on the East Coast,” said Jonathan Dean, director of communications for BWI, in an email.

Eventually, travelers will be able to book through the Southwest website, according to the company. For now, Southwest Rapid Rewards members can add their account to reservations on Icelandair and earn Rapid Rewards points for the Southwest portion of their journeys.

The interline partnership allows the two airlines to coordinate passengers (and their luggage) on an itinerary that uses multiple airlines, without requiring passengers to have multiple tickets.

“We’re grateful for the mutual confidence and enthusiasm that’s built a bridge between our two great airlines and aims to serve our customers and those of Icelandair on both sides of the Atlantic,” said Ryan Green, an executive vice president at Southwest Airlines, in a statement.

Icelandair is Southwest’s only interline partner right now, but the company’s website says it expects to add another partner airline this year.

Southwest is one of the country’s largest domestic airlines and uses BWI as a hub. It offers some international flights to destinations in Mexico, parts of Latin America and the Caribbean. The airline recently announced more direct flights from BWI to the West Coast — though all return flights from those destinations are red eyes.

Southwest already offers direct flights from Baltimore to western destinations, including Los Angeles, Salt Lake City, Phoenix and Las Vegas that operate daily, and not in red-eye hours.

Toward the end of 2024, Southwest announced it was doing away with its free-for-all seating method and assigning seats, and adding premium seating with extended legroom.

The company reported a net income of $465 million for 2024, which was about flat compared to the prior year.