Key West (Spanish: Cayo Hueso [kaʝo ˈweso]) is a coral cay island in the Straits of Florida, at the southernmost end of the U.S. state of Florida and its outlying Florida Keys archipelago. Together with all or parts of the separate islands of Dredgers Key, Fleming Key, Sunset Key, and the northern part of Stock Island, it constitutes the City of Key West.

For thousands of years, Key West and the surrounding islands were inhabited by various Native American tribes. The island's first recorded European contact occurred in 1513, when an expedition led by Spanish conquistador Juan Ponce de León circumnavigated the Florida Keys amid his voyage along the coast of Florida, though no permanent settlement was established. Over the following centuries, the island remained sparsely populated while passing between periods of Spanish and British control. Following the transfer of Florida to the United States in 1819, Key West rapidly developed into a major maritime center, with its strategic location along the Florida Straits and thriving wrecking industry helping make it one of the wealthiest communities in the United States during the 19th century.

Key West is the southernmost city in the contiguous United States and the westernmost island in the Florida Keys connected by highway, located about 130 miles (210 km) southwest of Miami and roughly 95 miles (153 km) north of Cuba. The island measures approximately 4 miles (6 km) long and 1 mile (2 km) wide, with a total land area of about 4.2 square miles (11 km²), and the city itself spans roughly 5.6 square miles (14.5 km²). It serves as the county seat of Monroe County, which includes a majority of the Florida Keys and part of the Everglades, and had a population of 26,444 at the 2020 census, carrying the motto “One Human Family.”

Key West functions as a major transportation and tourism hub, serving as the southern terminus of U.S. Route 1 and hosting a passenger cruise port, an international airport, and Naval Air Station Key West. Its main commercial corridor is Duval Street, which runs from the Gulf of Mexico to the Atlantic Ocean. Key West lies within the Florida Keys National Marine Sanctuary and is located near several protected areas, including the Dry Tortugas National Park and the Key West National Wildlife Refuge; due to its proximity to the Great Florida Reef, the island serves as a notable center for recreational diving.

The Conch Republic () is a micronation declared as a secession of the city of Key West, Florida, from the United States on April 23, 1982. It has been maintained as a tourism booster for the city. Since then, the term "Conch Republic" has been expanded to refer to "all of the Florida Keys, or, that geographic apportionment of land that falls within the legally defined boundaries of Monroe County, Florida, northward to 'Skeeter's Last Chance Saloon' in Florida City, Dade County, Florida, with Key West as the micronation's capital and all territories north of Key West being referred to as 'The Northern Territories'".

While the protests that sparked the creation of the Conch Republic (and others since then) have been described by some as "tongue-in-cheek", they were motivated by frustrations over genuine concerns. The original protest event was motivated by a U.S. Border Patrol roadblock and checkpoint that greatly inconvenienced residents and tourists.

The Conch Republic celebrates Independence Day every April 23 as part of a week-long festival of activities involving numerous businesses in Key West, including local rum distilleries like Chef Distilled. The organization—a "Sovereign State of Mind", seeking only to bring more "humor, warmth and respect" to a world in sore need of all three according to its late secretary general, Peter Anderson—is a key tourism booster for the area.