The thylacine (/ˈθaɪ.lə.siːn/, binomial name Thylacinus cynocephalus), also commonly known as the Tasmanian tiger or Tasmanian wolf, is an extinct carnivorous marsupial that was native to the Australian mainland and the islands of Tasmania and New Guinea. They had almost died out out on the Australian mainland from around 2,000 years ago, most likely because of the introduction of dingoes or due to climate change. Prior to European settlement around 5,000 remained in the wild on Tasmania. Beginning in the nineteenth century they were perceived as a threat to the livestock of farmers and bounty hunting was introduced. The last known of its species died in 1936 at Hobart Zoo in Tasmania. The thylacine is widespread in popular culture and is a cultural icon in Australia.

The thylacine was known as the Tasmanian tiger because it displayed dark transverse stripes that radiated from the top of its back, and it was known as the Tasmanian wolf because it had the general appearance of a medium-to-large-size canid. The name thylacine is derived from thýlakos meaning "pouch" and ine meaning "pertaining to", and refers to the marsupial pouch. Both genders had a pouch. The females used theirs for rearing young and the males used theirs as a protective sheath, covering the external reproductive organs. It also had a stiff tail and could open its jaws to an unusual extent. The thylacine was an apex predator, though exactly how large its prey had been is disputed. Its closest living relatives are the other members of Dasyuromorphia including the Tasmanian devil.

The thylacine had died out on New Guinea and very few were left on the Australian mainland before European settlement of the continent. Intensive hunting on Tasmania is generally blamed for its extinction, but other contributing factors were disease, the introduction of and competition with dingoes, human encroachment into its habitat and climate change. The remains of the last known thylacine were discovered at the Tasmanian Museum and Art Gallery in 2022. Since extinction there have been numerous searches and reported sightings of live animals, none of which have been confirmed.

The thylacine has been used extensively as a symbol of Tasmania. The animal is featured on the official coat of arms of Tasmania. On 7 September, the date in 1936 on which the last known thylacine died, National Threatened Species Day is commemorated in Australia. Universities, museums and other institutions across the world research the animal. Its whole genome sequence has been mapped and there are efforts to clone and bring them back to life.