Botany Bay is a bay in Sydney, New South Wales, Australia, a few kilometers south of the central business district. It was the site of a landing by James Cook of the HMS Endeavour that marked the beginning of Great Britain's interest in, and eventual colonisation of, Australia. In modern times it is chiefly notable for being the site of Kingsford Smith International Airport, Australia's largest.

The City of Botany Bay is the name of the local government area which encompasses suburbs adjacent to the bay (such as Botany, New South Wales) (before 1996, it was known as the Municipality of Botany).

The crew of the Endeavour became the first Europeans to visit the bay on 29 April 1770, when they landed on the southern Kurnell peninsula, making contact with the area's indigenous inhabitants. Cook originally named the bay Stingray Harbour. It was later renamed Botany Bay due to the diversity of new species of plant and animal discovered and catalogued by the expedition's botanist, Sir Joseph Banks. Banks was impressed by the site and recommended it an ideal site for a British colony.

In 1788, Captain Arthur Phillip led the First Fleet into the bay on 19 January 1788 to found a penal colony there. Finding that the sandy infertile soil of the site in fact rendered it most unsuitable for settlement, Phillip decided instead to move to the excellent natural harbor of Port Jackson to the north. On 26 January, while still anchored in the bay, the British encountered the French exploratory expedition of Jean-François de La Pérouse. Panicked by the thought that the French might beat them to it, the colonists sailed that afternoon to found a settlement at Sydney Cove. Despite the move, for many years afterward, the Australian penal colony would be referred to as "Botany Bay" in England - in convict ballad s, for instance.

The good supply of fresh water in the area led to the expansion of its population in the 19th century.

The small Mascot Aerodrome at Botany developed into Sydney (Kingsford Smith) Airport. Port Botany was built in 1930 and is now a container terminal.