Philadelphia International Airport opened on June 20, 1940, as Philadelphia Municipal Airport, built on land the city had been assembling since the mid-1920s, including a $3 million purchase of the derelict Hog Island Shipyard along the Delaware River. Construction delays caused by the Great Depression pushed the project back to 1937, and the original terminal was a modest $110,000 wooden structure. It handled roughly 40,000 passengers in its inaugural year, primarily on Douglas DC-3 aircraft. World War II forced a suspension of commercial service from late 1943, and the airport returned to civilian hands in 1945, the same year American Overseas Airlines inaugurated transatlantic service to London, prompting the city to rename it Philadelphia International Airport.

Today, PHL sits 7 miles southwest of Center City Philadelphia, pressed between Interstate 95 and the Delaware River, with four runways and seven terminals arranged in a continuous linear row, an unusual layout that allows passengers to walk the entire airside concourse without re-clearing security. American Airlines is by far the dominant carrier, commanding more than 60% of passenger traffic and operating PHL as its primary transatlantic gateway, connecting the hub to European cities including London, Paris, Amsterdam, Dublin, and a growing list of secondary markets made viable by newer narrow-body long-haul aircraft. UPS Airlines operates a regional cargo hub at the airport, and Frontier Airlines uses it as a focus city.

The airport serves the broader Delaware Valley, a region of approximately 6 million people across 9 counties in Pennsylvania and southern New Jersey. Passenger volume reached roughly 30 million annually in recent years. Its position on the Northeast Corridor, with direct SEPTA rail access, makes it one of the more intermodally connected major airports in the United States.