Ottawa International Airport (IATA: YOW) or Ottawa/Macdonald-Cartier International Airport is located in Riverside South, 5.5 nm south of downtown Ottawa. It's part of Canada's busiest air corridor between Ottawa, Montreal, and Toronto, commonly called the Eastern Triangle. The airport is also a gateway for flights to the eastern Arctic via Iqaluit.

Ottawa International Airport is a home base for Canadian North and a hub for Porter Airlines.

Nav Canada classified it as an airport of entry, and the Canada Border Services Agency staffed it. YOW is one of eight Canadian airports with United States border preclearance facilities. The airport was formerly a military base known as CFB Ottawa South/CFB Uplands and is still home to the Royal Canadian Air Force's (RCAF) 412 Transport Squadron, which provides air transport for Canadian and foreign government officials.

At the turn of the millennium, the Ottawa Airport Authority announced plans to build a second, adjacent terminal to meet the demands of increased traffic. The terminal, designed by architect Richard Brisbin, was completed ahead of schedule and opened in October 2003. This terminal building now handles all airline passenger traffic. A section of the 1960 terminal, which was connected to the new terminal by an enclosed bridge, was still used at peak times of the day when extra gate space was needed, and it also handled most domestic regional flights. Funding for the terminal construction was collected from the parking meters outside the terminal beginning in January 1997, when rates were hiked to cover the costs of a new terminal building.

The old terminal and tower, built in 1960, was a modernist International style designed by architects James Strutt, and William Gilleland and by Transport Canada architect W.A. Ramsay. They had been heavily renovated and modernized in 1985–87, which included the removal of a seating area containing personal television screens which would provide 15 minutes of VHF TV channels for 25 cents, as well as an open ceiling design. They were demolished in 2008 to make way for Phase II of the new terminal.

Ottawa International Airport's board of directors approved a further expansion of the airport's passenger terminal on April 4, 2006. The extension of the new terminal was built in phases by Brisbin Brook Benyon and Architecture. Phase II, the next phase of the expansion program opened March 13, 2008. This addition contains over 7,000 m2 of space and adds twelve gates and seven jetways.

Ottawa International Airport currently has European connections to Paris–Charles de Gaulle and a future seasonal connection to London–Heathrow on March 31, 2025. It previously had a connection to Frankfurt.

In September 2019, Canadian flag carrier Air Canada announced that it would shut down its seasonal daily route between Ottawa and Frankfurt in Germany, a key Star Alliance hub. However, Lufthansa announced a plan to begin flights from Frankfurt to Ottawa airport five times a week from May 2020. This plan did not materialize though, when the airport lost all nonstop transatlantic routes to Europe due to the pandemic in March 2020.

On June 27, 2023, Air France began a new, year-round route connecting Ottawa with its main hub, at Paris–Charles de Gaulle, with service offered five times weekly. First by Airbus A330-200, then with Boeing 787-9 Dreamliner, flights are operated with an Airbus A350-900XWB aircraft since April 7, 2024.