Biloxi is a city located in Harrison County, Mississippi, United States, situated on the Gulf Coast in southern Mississippi. It lies directly on the Mississippi Sound, with barrier islands scattered off the coast into the Gulf of Mexico, and borders the city of Gulfport to its west. Both Biloxi and Gulfport are designated as seats of Harrison County. The area is also partially bordered by Biloxi Bay to the northeast, which forms part of the Jackson County line.

The region's first European settlement was established in 1699 by French colonists under Pierre Le Moyne d'Iberville at Fort Maurepas, now Ocean Springs, referred to as Old Biloxi. The current city site was settled around Fort Louis in 1720, serving as the capital of French Louisiana until 1722. Following periods of British and Spanish rule, the area became part of the Mississippi Territory in 1811 and Mississippi was admitted to the union in 1817. Biloxi was incorporated in 1838.

The city is home to Keesler Air Force Base, housing the 81st Training Wing and the 403rd Wing of the U.S. Air Force Reserve. Notable landmarks include the Biloxi Lighthouse, completed in May 1848, and the Jefferson Davis Presidential Library and Museum. The beachfront lies on the Mississippi Sound, and the city features nine casinos, including the Beau Rivage and Hard Rock Hotel. Edgewater Mall was built in 1963, and a memorial to Katrina victims stands as a site of remembrance.

Biloxi gained fame as a summer resort in the antebellum period due to its breezes and beaches, attracting wealthy slave-owners and commercial figures. The seafood industry developed rapidly after the first cannery opened in 1881, leading to the city being termed the seafood capital of the world by 1900. The tradition of blessing fishing boats began here in 1929. In the 1990s, legal gambling transformed the economy, drawing millions in tourism revenue and establishing the region as a leading gambling center.

The population was 49,449 at the 2020 census, making it the state's fourth-most populous city. It is a principal city of the Gulfport–Biloxi metropolitan area, which had 416,259 residents in 2020. The economy boomed during World War II and again with the casino industry. The area is prone to hurricanes, notably Katrina in 2005, which caused massive damage. The city continues to implement plans for commercial redevelopment south of Highway 90.