South Philadelphia, nicknamed South Philly, is the section of Philadelphia bounded by South Street to the north, the Delaware River to the east and south, and the Schuylkill River to the west. A diverse working-class community of many neighborhoods, South Philadelphia is well known for its large Italian-American population, though it also contains large Asian-American, Irish-American, African-American, and Latino populations.

South Philadelphia began as a satellite town of Philadelphia, with small townships such as Moyamensing and Southwark. Towards the end of the First Industrial Revolution, the area saw rapid growth in population and urban development. This expansion was in part due to an influx of working class laborers and immigrants looking for factory jobs and dock work, as well as the first wave of mass immigration of Irish refugees or impoverished immigrants from Ireland in the wake of the Great Irish Hunger. South Philadelphia's urbanized border eventually expanded to reach that of Philadelphia proper, or what is today known as Center City Philadelphia. Along with all other jurisdictions in Philadelphia County, South Philadelphia became part of the City of Philadelphia proper with passage by the Pennsylvania legislature of the city–county Act of Consolidation, 1854.

The area continued to grow, becoming a vital part of Philadelphia's large industrial base and attracting immigrants from Italy, Ireland, Poland and many Southern European and Eastern European countries during the late 19th and early to mid 20th centuries, as well as Black American migrants from the southern United States during the Great Migration of the early 20th century. The immigrants and migrants became the basis of South Philadelphia's unique and vibrant culture that developed over the next several decades. Struggling to maintain their Catholic identity in a mostly Protestant city, the Irish built a system of Irish Catholic churches and parochial schools for their children, including Catholic high schools. The later immigrant populations of Italians and Poles were also Catholic. Initially, these populations attended existing Catholic churches but built their own ethno-national churches when possible. However, the more established Irish-American ethnic community controlled the Catholic clergy and hierarchy for decades in Philadelphia and throughout the region, often excluding the more recent Italian (and, to a lesser extent, Polish) populations from participating in the church hierarchy.

In addition to the influx of Catholic immigrants to the majority Protestant city of Philadelphia, many Polish Jews and other Jews from Central and Eastern Europe settled in South Philadelphia during the first half of the 20th century, especially in the diverse area now known as Queen Village where Jewish immigrants lived among Catholic Polish immigrants, Irish-Americans, and Italian immigrants. A smaller but significant Greek immigrant community also flourished around this time, leading to the establishment of Greek Orthodox parishes in South Philadelphia, while Lebanese immigrants established Lebanese Maronite parishes. Despite this dramatic growth in population, the low funding of education by the city resulted in the first public high school not being formed in South Philadelphia until 1934.

Attracted to the industrial jobs, the new residents of South Philadelphia created communities that continued many of their Old World traditions. While many of the new arrivals were Catholic, neighborhood parishes reflected their ethnic and national traditions. Monsignor James F. Connelly, the pastor of the Stella Maris Catholic Church and an editor of the 1976 work The History of the Archdiocese of Philadelphia, said in a 2005 Philadelphia Inquirer article that each parish church "offer[s] the immigrants the faith they were familiar with." Coptic Orthodox Christian churches were also established in South Philadelphia in the 1960s. With the dramatic loss of industrial jobs during mid-20th century restructuring, there were population losses in South Philadelphia as well as other working-class parts of the city, and some neighborhood Catholic schools had to close.

Today, many of South Philadelphia's communities are largely Italian Americans. Many of these communities contain both older and more recent Italian immigrants and Italian speakers, and Italian saint festivals and cultural celebrations, including the South 9th Street Italian Market festival, are popular in the South Philadelphia Italian-American communities. In addition, South Philadelphia continues to be home to many ethnic Irish American communities and African American communities. Both Irish American and African American communities can be found in the neighborhoods of Grays Ferry and Southwest Center City, while the nearby neighborhood of Point Breeze is largely African American and is often considered the center of the South Philadelphia's African American communities. The neighborhood of Pennsport remains primarily a working class Irish-American neighborhood and the cultural center of Irish-American South Philadelphia. An increase in late 20th-century and early 21st-century immigration has given South Philadelphia significant populations from Asia, particularly Southeast Asia, including populations from Vietnam, Cambodia, Indonesia and Thailand. In addition, there has been an increase in recent years of immigrants from Russia, Mexico and Central American nations such as Honduras, Guatemala and El Salvador. Today, many vendors that work alongside the Italian-Americans at the Italian Market are of Asian descent and Mexican or Central American descent, and Vietnamese, Thai, Mexican, and Central American restaurants are interspersed with historic Italian restaurants in the Market area. The recent revitalization of Center City Philadelphia and the subsequent gentrification of adjacent neighborhoods has also led to dramatic rises in prices of housing in the neighborhoods of historic Queen Village, Bella Vista, and some other northern parts of South Philadelphia, leading to an influx of young urban professionals in those more northern neighborhoods.

Many of the community clubs that create the annual Mummers Parade every New Year's Day have traditionally been from South Philadelphia, especially those located on the largely Irish-American S. 2nd Street ("Two Street") in the Pennsport neighborhood.

Portions of South Philadelphia are within Philadelphia City Council Districts 1 and 2. As of 2014 Councilman Mark Squilla and Councilman Kenyatta Johnson represent the two districts.