Fernandina Beach is a city in Nassau County, Florida, United States, on Amelia Island. It is the northernmost city on Florida's Atlantic coast, and is one of the principal municipalities comprising Greater Jacksonville. The area was first inhabited by the Timucuan Indian tribe. Located on Amelia Island, known as the "Isle of 8 Flags", Fernandina has had the flags of the following nations flown over it since 1562: France, Spain, Great Britain, Spain (again), the Patriots of Amelia Island, the Green Cross of Florida, Mexico, the Confederate States of America, and the United States. It is the only municipality in the United States that has flown eight different national flags.

According to the 2010 census, the city population was 11,487. It is the seat of Nassau County.

Prior to the arrival of Europeans on what is now Amelia Island, the site of the original town of Fernandina was occupied by Native Americans. Native American bands associated with the Timucuan mound-building culture had settled on the island about A.D. 1000, calling it Napoyca. They remained on the island until the early 18th century, when European settlement began there. In 1736, James Oglethorpe, the governor of Georgia, ordered Fort Amelia to be built at the mouth of the St. Marys River to house a garrison of Scottish Highlanders. The American naturalist William Bartram visited Amelia Island in 1774, noting the presence of several very large tumuli, or earthwork mounds, which the colonists called "Ogeechee mounts". France, England, and Spain all had maintained a presence on the island intermittently during the 16th through 18th centuries, but the first permanent European settlement was not made until Spain took over Florida from Britain at the end of the American Revolution. During later colonial times the site had gained military importance because of its deep harbor and its strategic location near the northern boundary of Spanish Florida. On January 1, 1811, Enrique White, governor of Spain's East Florida province, named the town of Fernandina, about a mile from the present city, in honor of King Ferdinand VII. On May 10 of that year, Fernandina became the last town platted under the Laws of the Indies in the Western hemisphere. The town was intended as a bulwark against U.S. territorial expansion. In the following years, it was captured and recaptured by a succession of renegades and privateers. The proclamation of the Adams-Onis Treaty on February 22, 1821, two years after its signing in 1819, officially transferred Spain's territories in Florida, including Amelia Island, to the United States.

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