Andros Island is an archipelago within the Bahamas, the largest of the Bahamian Islands. Politically considered a single island, Andros in total has an area greater than all the other 700 Bahamian islands combined. The land area of Andros consists of hundreds of small islets and cays connected by mangrove estuaries and tidal swamplands, together with three major islands: North Andros, Mangrove Cay, and South Andros. The three main islands are separated by "bights", estuaries that trifurcate the island, connecting the island's east and west coasts. It is 104 miles (167 km) long by 40 miles (64 km) wide, at the widest point.

Noteworthy for a unique combination of marine features and ecosystems, Andros is bordered on the east by the 6000 foot (3+ km) deep Tongue of the Ocean. The Andros Barrier Reef is the world's sixth longest. It runs for 142 miles (225 km), averaging a distance of 1–2 miles from the Andros shore. The extensive flats of the Great Bahama Bank lie to the west, northwest and south of Andros. The island has the world's largest collection of blue holes.

Geographically, North Andros is the sixth largest island in the West Indies, at roughly 6,000 km2 (2,300 sq mi) in area and 167 km (104 mi) long and 64 km (40 mi) wide at its widest point, and the 153rd largest island on Earth. If all three main islands are included, Andros is the fifth-largest island in the West Indies, after Cuba, Hispaniola, Jamaica and Puerto Rico. Although comparable in total area to the state of Rhode Island (3140 km2, population 1.05 million) together with Long Island, New York (3600 km2, population 7.5 million), Andros only has a population of approximately 8000, almost all of whom are settled in a thin strip near the Queen Elizabeth Highway running along the island's eastern coast.

Andros is 30 miles (48 km) west across the Tongue of the Ocean from the Bahamas' national capital of Nassau on New Providence Island. Its northern tip lies 138 miles (233 km) from Fort Lauderdale, Florida. Geologically and geographically the Bahamas, including Andros, are not located in the Caribbean, whose northern boundary is the Windward Passage, but rather in the Atlantic Ocean. Historically, the nation was part of the British West Indies and is considered culturally to be part of the Caribbean. The Bahamian dialect of the English language is distinctively Caribbean in character, similar to those of Jamaica and the Cayman Islands, also formerly part of the British West Indies.

The township of Fresh Creek is home to the Atlantic Undersea Test and Evaluation Center (AUTEC), operated by the United States Navy. The United Kingdom and United States conduct special operations training, and sonar and submarine research in the Tongue of the Ocean. The United States Coast Guard also runs rescue and drug interdiction operations from AUTEC.

Andros is known in the Bahamas by two nicknames, "The Sleeping Giant" and "The Big Yard".