The giant cuttlefish, also known as the Australian giant cuttlefish, is the world's largest cuttlefish species, growing to 50 cm (20 in) in mantle length and up to 100 cm (39 in) in total length. They can be over 10.5 kg (23 lb) in weight. Using cells known as chromatophores, the cuttlefish can put on spectacular displays, changing color in an instant. The giant cuttlefish is native to temperate and subtropical waters of Australia, from Brisbane in Queensland to Shark Bay in Western Australia and Tasmania to the south. It occurs on rocky reefs, seagrass beds, and sand and mud seafloor to a depth of 100 m (330 ft). In 2009 the species was listed at Near Threatened on the IUCN Red List of Threatened Species due to an observed declining trend at that time.

Cuttlefish, or cuttles, are marine molluscs of the order Sepiida. They belong to the class Cephalopoda which also includes squid, octopuses, and nautiluses. Cuttlefish have a unique internal shell, the cuttlebone, which is used for control of buoyancy.