Fountain Square (abbreviated as FSQ) is a neighborhood and designated cultural district in Indianapolis, Indiana, United States. Located approximately 1+1⁄2 miles (2.4 km) southeast of downtown Indianapolis, Fountain Square is home to three designated national historic districts, the Laurel and Prospect, the State and Prospect, and the Virginia Avenue districts, all of which were listed on the National Register of Historic Places in 1983. The neighborhood derives its name from the successive fountains that have been prominently featured at the intersection of Virginia Avenue, East Prospect Street, and Shelby Street.

Fountain Square is the first commercial historic district in Indiana, and it is the only portion of the city outside the initial mile square that has continually operated as a recognized commercial area since the 1870s. Its significance is not only as an early commercial district, but additionally as one developed and dominated by German-American immigrants, merchants, and entrepreneurs, who established a strong German character on the city's southside. From the 1920s to the 1950s, Fountain Square was the city's main entertainment district, with as many as seven theaters in operation at one point in time.

In the late 1960s and early 1970s, a large swath of Fountain Square was demolished to complete the Interstate Highway System in Indianapolis, leaving the remaining neighborhood disconnected from the surrounding area. After decades of population decline, the neighborhood is estimated to have 9,839 inhabitants. Historic preservation efforts began in the late 1990s, and the neighborhood slowly re-emerged as a vibrant commercial center. Today, Fountain Square is widely considered to be Indianapolis's newest trendy neighborhood, with an eclectic mix of retro architecture and modern, urban design.

Although Fountain Square is not officially delineated, the Fountain Square Neighborhood Association's service area is bounded to the north by the railroad tracks north of Deloss Street, to the east by State Street, to the south by Pleasant Run Parkway, and to the west by I-65. It is located 1.5 miles (2.4 km) southeast of downtown Indianapolis, and covers an area of approximately 1 square mile (2.6 km²). Little remains of the original geographic features of the land.

Fountain Square bases a portion its street pattern due to a continuation of the diagonal Virginia Avenue, which came about from the 1821 Ralston Plan for the new city of Indianapolis. The neighborhood is bordered upon by Bates–Hendricks to the southwest, Fletcher Place to the northwest, and Holy Cross neighborhood to the north. Within its boundaries, it houses the Laurel and Prospect, State and Prospect, and the Virginia Avenue historic districts.

Prior to the arrival of Fountain Square's modern-day inhabitants, the area was inhabited by the Delaware people, who settled there after they were pushed out of their homeland along the Delaware River watershed. After the Treaty of St. Mary's was signed on October 3, 1818, the Delaware ceded their lands in Indiana, which included a camp site at Pleasant Run, near Fountain Square's modern-day southern boundary. By 1820, the Delaware people were gone.

In 1835, Calvin Fletcher, a banker, farmer and Indiana state senator, purchased a 264-acre (107 ha) farm with Nicholas McCarty, with the intent to "sell the small parcels for a 'handsome advance'". While the early settlement was sparsely populated and primarily residential, the areas surrounding modern-day Fountain Square saw an influx of immigrants, particularly the Irish, who settled near the railroad tracks on South Street. Eventually, this area became known as "Irish Hill".

During the 1860s, the Virginia Avenue corridor began to emerge as the southside's commercial district. During the Civil War, the 28th Colored Infantry Regiment, which was the only black regiment formed in Indiana, trained at a wooded area at Indianapolis's Camp Fremont, on land owned by Calvin Fletcher. It included 518 enlisted men who signed on for three years of service.