Forget what you know about getting your groups to Europe. The Open Skies Agreement between the United States and the European Union, which takes effect at the end of March, will eliminate decades of restrictions on the trans-Atlantic airline market.

Under the accord, U.S. and EU airlines will be able to operate to and from any airport, and U.S. carriers will be able to fly within Europe and continue on to other destinations. EU airlines have not won the right to operate intra-U.S. flights.

Among the destinations most affected will be London’s Heathrow airport, which, since 1977, has been operating under the Bermuda 2 agreement, which allows only four airlines—British Airways, Virgin Atlantic, American, and United—to fly between Heathrow and the U.S. At the end of March, Heathrow’s new Terminal 5 will open as the new home to the vast majority of British Airways’ flights, freeing up some space at the busy airport. Northwest, Continental, and Delta all plan to get a toehold at Heathrow under the new liberalization policy. Here’s a sample of the changes that Open Skies has set in motion:

• In June, British Airways plans to launch a U.S.-EU subsidiary airline, called OpenSkies, with daily flights from New York to either Brussels or Paris. A second route will be added later in the year to the other destination.
• Aer Lingus launched service early this year from Dublin to Washington, D.C.; Orlando, Fla.; and San Francisco. (It got a jump on Open Skies through an arrangement between the Irish and U.S. governments.) Aer Lingus also has a new partnership with JetBlue Airways. Starting April 3, passengers will be able to book linked flights between Ireland and more than 40 U.S. destinations, connecting through New York's Kennedy International.
• Continental will be using Heathrow for the first time for flights from Newark, N.J., and Houston.
• British Airways plans to move its Dallas and Houston flights from Gatwick to Heathrow and cut its Detroit route.
• Detroit will have new Heathrow service from Northwest Airlines starting this spring, and the airline plans to launch daily Heathrow flights from Minneapolis-St. Paul and Seattle.
• Delta—in partnership with Air France-KLM—will fly from Heathrow to New York and Atlanta, while Air France-KLM plans a new Heathrow-Los Angeles route.