Philadelphia ( /ˌfɪlədɛlfiə/) is the largest city in the Commonwealth of Pennsylvania and the county seat of Philadelphia County, with which it is coterminous. The city is located in the Northeastern United States along the Delaware and Schuylkill rivers and it lies about 80 miles (130 km) southwest of New York City. It is the fifth-most-populous city in the United States, with a 2010 U.S. Census estimated population of 1,526,006. Philadelphia is also the commercial, cultural, and educational center of the Delaware Valley, home to 6 million people and the country's fifth-largest metropolitan area. Popular nicknames for Philadelphia are Philly and The City of Brotherly Love, the latter of which comes from the literal meaning of the city's name in Greek (Greek: Φιλαδέλφεια ([pʰiladelpʰeːa], Modern Greek: [filaðelfia]) "brotherly love", compounded from philos (φίλος) "loving", and adelphos (δελφός) "brother").

Philadelphia was founded on October 27, 1682 by William Penn, who planned a city along the Delaware River to serve as a port and place for government. The city grew rapidly, and by the 1750s Philadelphia was the largest city and busiest port in the original 13 American colonies. During the American Revolution, Philadelphia played an instrumental role as a meeting place for the Founding Fathers of the United States, who signed the nation's Declaration of Independence on July 4, 1776 and the Constitution on September 17, 1787. Philadelphia served as one of the nation's many capitals during the Revolutionary War, and the city served as the temporary national capital from 1790 to 1800 while Washington, D.C. was under construction. During the 19th century, Philadelphia became a major industrial center and a railroad hub that grew from an influx of European immigrants. The city's dominant textile industry represented 40 percent of total United States output in 1906. It became a major destination for African Americans during the Great Migration and surpassed 2 million occupants by 1950.

Philadelphia has transitioned from being a manufacturing powerhouse to an information and service-based economy. Financial activities account for the largest sector of the metro economy, and it is one of the largest health education and research centers in the United States. Philadelphia's history attracts many tourists, with the Liberty Bell receiving over 2 million visitors in 2010. The Delaware Valley contains the headquarters of thirteen Fortune 500 corporations, five of which are in Philadelphia proper. With a gross domestic product of $388 billion, Philadelphia ranks ninth among world cities and fourth in the nation. The city is also the nation's fourth-largest consumer media market, as ranked by the Nielsen Media Research.

