South Street in Philadelphia, initially named Cedar Street in William Penn's original street grid, is an east–west street forming the southern border of Center City and the northern border for South Philadelphia in Pennsylvania, United States.

The South Street Headhouse District between Front and 7th or 8th streets is a neighborhood known for its bohemian, punk, and alternative atmosphere and its diverse urban mix of shops, bars, and eateries. South Street is one of Philadelphia's largest and most prominent tourist attractions.

Originally the southern border of William Penn's 1682 city plan and officially named Cedar Street until 1854, eastern South Street had been originally the center of local Swedish and Dutch populations, then Irish in the early to mid 1800s, and, many decades later, Jewish and Italian immigrant culture as well as a vibrant African-American neighborhood.

Because Quaker doctrine opposed live performances within the city limits, the first permanent theater in the United States was built on the south side of the street at Leithgow Street, giving birth to a tradition of Philadelphians seeking out entertainment on South Street that continues today.

In 1854, the same year that South Street officially became South Street, the city boundaries were redrawn to expand the area of Philadelphia to 130 square miles.

Despite no longer being a literal border, South Street remained a liminal space where cultures collided. The African American theater district of western South Street, the later Jewish and Italian immigrant shops and theaters on eastern South Street, the nearby Italian businesses in the Italian Market area, and the influx of visitors from other parts of the city looking for entertainment all combined to eventually create a place described by William Gardner Smith in his 1954 book South Street as a lively zone of contact between many different ethnicities.

Until the 1950s, South Street was known mainly as a multiethnic entertainment and garment district, with an abundance of stores for men's suits and other clothing. The eastern end of South Street comprised part of the Jewish and Italian Fabric Row, while the more western areas around South Street served as a cultural and commercial center for South Philadelphia's African American community.

Real estate values plummeted after city planner Edmund Bacon and others proposed the Crosstown Expressway, a short limited-access expressway connecting the Schuylkill Expressway and I-95 that would have required the demolition of many buildings on South Street and Bainbridge Street (an east–west street one block south of South Street). The suddenly cheap property attracted artists and counterculture-types. The proposed expressway was never built due to public opposition.