Center City is the term used in the local vernacular to refer to Philadelphia's "downtown" central business district (CBD). It is traditionally considered to be bounded by South Street to the south, the Delaware River to the east, the Schuylkill River to the west and either Spring Garden Street or the more southerly Vine Street. (If the latter is to be considered the northern border, then Center City corresponds exactly to the original city of Philadelphia as it existed prior to the consolidation of all of Philadelphia County into the city in 1854.)

Center City's many districts and residential neighborhoods include Penn's Landing, Old City (the historic district and the site of numerous art galleries and collectives, and a number of bars and restaurants), Society Hill, Washington Square West, Market East, Chinatown, Logan Circle, the Museum District (located along the Ben Franklin Parkway), Rittenhouse Square, the Avenue of the Arts (South Broad Street), and Jewelers' Row.

The majority of Philadelphia's skyscrapers are located in Center City. Philadelphia's City Hall is the tallest masonry building in the world; the largest municipal building in the world; and, through the late 1980s, was the tallest building in Philadelphia until the construction of the Liberty Place complex. In March of 1987, One Liberty Place broke the "gentlemen's agreement" not to exceed the height of the statue of William Penn on the top of the City Hall. To date, only buildings behind the "back" (to the west) of the Penn statue rise above its height; those in its "field of vision" (to the east) do not.

Since the construction of One Liberty Place, seven other skyscrapers have been completed exceeding the height of the statue, including One Liberty Place's little sister, Two Liberty Place. One Liberty Place is the tallest building in the state, but in 2005 construction began on the Comcast Center which, when completed in 2007, will be 30 feet taller than One Liberty Place. Three additional buildings currently proposed for construction to the west of City Hall, Mandeville Place, 1441 Chestnut, and Bridgeman's View Tower, will also be taller than City Hall upon completion.

Other Philadelphia skyscrapers include the Mellon Bank Center and the Verizon Tower, the latter housing a traffic camera used by the Philadelphia branch of the Westwood One MetroNetworks traffic service.

Across the street from City Hall is a Masonic Temple, the Grand Lodge of Pennsylvania, a legacy of the Founding Fathers and signers of the Declaration of Independence, many of whom were Freemasons, such as George Washington and Benjamin Franklin.

While Philadelphia as a whole has experienced a population decline since the 1960s, Center City has become a fast-growing section of the city. Between the 1990 and 2000 censuses, the population of Center City increased by 10%. The 2005 Center City population, at approximately 90,000, makes Center City one of the more populated central business districts in the United States.