Philadelphia International Airport (IATA: PHL, ICAO: KPHL, FAA LID: PHL) is an airport in Philadelphia, Pennsylvania, and is the largest airport in the Delaware Valley region. As of 2008 it is the 10th busiest airport in the world in terms of aircraft activity. The airport is the primary international hub of US Airways and has service to destinations in the United States, Canada, the Caribbean, Latin America, Europe, and soon China when US Airways begins service to Beijing in March of 2009.

Today, Philadelphia International Airport is one of the busiest airports in the world and among the fastest growing in the United States. Its status as a US Airways hub and the growth of Southwest Airlines and other low-cost carriers has helped passenger traffic to reach record levels. In 2004, a total of 28,507,420 passengers flew through Philadelphia, up 15.5% over 2003. In 2005, 31,502,855 passengers flew through PHL, marking a 10% increase since 2004.

The Philadelphia metropolitan area is the fourth largest in the U.S. by the current official definition, with some 5.8 million people.

Philadelphia is one of the oldest and most historically significant cities in the United States. During part of the 18th century, the city was the second capital and most populous city of the United States, and the second largest English speaking city in the world after London. At that time, it eclipsed Boston and New York City in political and social importance, with Benjamin Franklin playing an extraordinary role in Philadelphia's rise.