Tarbosaurus (/ˌtɑːrbəˈsɔːrəs/ TAR-bə-SOR-əs; meaning "alarming lizard") is a genus of large tyrannosaurid dinosaur that lived in Asia during the Maastrichtian age of the Late Cretaceous epoch. It contains the type and single species Tarbosaurus bataar, which is known from the Nemegt Formation of Mongolia, with more fragmentary remains found further afield in the Subashi Formation of China. Tarbosaurus is represented by dozens of fossil specimens, including several complete skulls and skeletons. These remains have allowed studies focusing on its phylogeny, skull mechanics, and brain structure. Further fossil remains have been reported from other geologic formations of Asia, however, these remains are fragmentary and cannot be confidently assigned to Tarbosaurus or the type species.

Like most known tyrannosaurids, Tarbosaurus was a large bipedal predator, with the type specimen measuring approximately 10 metres (33 ft) long, 3 metres (9.8 ft) tall at the hips, and weighing up to 4.5–5 metric tons (4.4–4.9 long tons; 5.0–5.5 short tons). It had a unique locking mechanism in its jaw, equipped with about sixty large teeth, and the smallest arms relative to body size of all tyrannosaurids, renowned for their disproportionately tiny, two-fingered hands.

Although many species have been named, most modern paleontologists recognize only one species, T. bataar. Some experts see this species as an Asian representative of the North American genus Tyrannosaurus, which would make the genus Tarbosaurus redundant. Tarbosaurus and Tyrannosaurus, if not synonymous, are considered to be very closely related genera. Alioramus, also from Mongolia, has previously been thought by some authorities to be the closest relative of Tarbosaurus, though this has since been disproven with the discovery of Qianzhousaurus and the description of the tyrannosaurine tribe Alioramini.

Tarbosaurus lived in a humid floodplain dominated by deserts, forests, and plains, and criss-crossed by river channels. It was an apex predator in this environment, preying on other large dinosaurs including ankylosaurids, such as Tarchia and Saichania, hadrosaurids, such as Saurolophus and Barsboldia, and sauropods, such as Nemegtosaurus and Opisthocoelicaudia.

In 1946, a joint Soviet-Mongolian expedition to the Gobi Desert in the Ömnögovi Province turned up a large theropod skull and some vertebrae from the Nemegt Formation. In 1955, Evgeny Maleev, a Soviet paleontologist, made this specimen the holotype (PIN 551–1) of a new species, which he called Tyrannosaurus bataar. The specific name is a misspelling of the Mongolian word баатар/baatar, meaning "hero". In the same year, Maleev also described and named three new theropod skulls, each associated with skeletal remains discovered by the same expedition in 1948 and 1949. The first of these, PIN 551–2, was named Tarbosaurus efremovi, a new generic name composed of the Ancient Greek words τάρβος (tarbos), meaning "terror", "alarm", "awe", or "reverence", and σαυρος (sauros), meaning "lizard", and the species was named after Ivan Yefremov, a Russian paleontologist and science fiction author. The other two, PIN 553-1 and PIN 552–2, were also named as new species and assigned to the North American genus Gorgosaurus as G. lancinator and G. novojilovi, respectively. All three of these latter specimens are smaller than the first.

A 1965 paper by A. K. Rozhdestvensky recognized all of Maleev's specimens as different growth stages of the same species, which he believed to be distinct from the North American Tyrannosaurus. He created a new combination, Tarbosaurus bataar, to include all the specimens described in 1955 and newer material. Later authors, including Maleev himself, agreed with Rozhdestvensky's analysis, although some used the name Tarbosaurus efremovi instead of T. bataar.

American paleontologist Ken Carpenter re-examined the material in 1992. He concluded that it belonged to the genus Tyrannosaurus, as originally published by Maleev, and lumped all the specimens into the species Tyrannosaurus bataar (except the remains that Maleev had named Gorgosaurus novojilovi). Carpenter thought this specimen represented a separate, smaller genus of tyrannosaurid, which he called Maleevosaurus novojilovi. George Olshevsky, Tracy Ford and Seiji Yamamoto created the new generic name Jenghizkhan (after Genghis Khan) for Tyrannosaurus bataar in 1995, while also recognizing Tarbosaurus efremovi and Maleevosaurus novojilovi, for a total of three distinct, contemporaneous genera from the Nemegt Formation. A 1999 study subsequently reclassified Maleevosaurus as a juvenile Tarbosaurus. Most research published since 1999 recognizes only a single species, which is either called Tarbosaurus bataar or Tyrannosaurus bataar, although some scholars suspect that there could be a second species.

After the original Soviet-Mongolian expeditions in the 1940s, Polish-Mongolian joint expeditions to the Gobi Desert began in 1963 and continued until 1971, recovering many new fossils, including new specimens of Tarbosaurus from the Nemegt Formation. Expeditions involving Japanese and Mongolian scientists between 1993 and 1998, as well as private expeditions hosted by Canadian paleontologist Phil Currie around the turn of the 21st century, discovered and collected even more Tarbosaurus material. More than 30 specimens are known, including more than 15 skulls and several complete postcranial skeletons.