Acrocanthosaurus (/ˌækroʊˌkænθəˈsɔːrəs/ AK-roh-KAN-thə-SOR-əs; lit. 'high-spined lizard') is a genus of carcharodontosaurid dinosaurs that existed in what is now North America during the Aptian and early Albian stages of the Early Cretaceous, from 113 to 110 million years ago. Like most dinosaur genera, Acrocanthosaurus contains only a single species, A. atokensis. It had a continent-wide range, with fossil remains known from the U.S. states of Oklahoma, Texas, and Wyoming in the west and Maryland in the east. However, most of these remains are assigned to the species based on the assumption that Acrocanthosaurus is the only large carcharodontosaurid from North America during this time, and the possibility exists that some referred specimens could represent distinct taxa.

Acrocanthosaurus was a bipedal predator. As the name suggests, it is best known for the high neural spines on many of its vertebrae, which most likely supported a ridge of muscle over the animal's neck, back, and hips. Acrocanthosaurus was one of the largest theropods, with the largest known specimen reaching 11–11.5 metres (36–38 ft) in length and weighing about 4.4–8.4 metric tons (4.9–9.3 short tons). Large theropod footprints discovered in Texas may have been made by Acrocanthosaurus, although no direct association with skeletal remains has been found. Recent discoveries have elucidated many details of its anatomy, allowing for specialized studies focusing on its brain structure and forelimb function. Acrocanthosaurus was the largest theropod in its ecosystem and likely an apex predator that preyed on sauropods, ornithopods, and ankylosaurs.

Acrocanthosaurus is named after its tall neural spines, from the Greek ἄκρος/ákros (high), ἄκανθος/ákanthos (thorn or spine), and σαῦρος/saũros (lizard). The lone named species (A. atokensis), is after Atoka County in Oklahoma, where the original specimens were found. The name was coined in 1950 by American paleontologists J. Willis Stovall and Wann Langston Jr. Langston had proposed the name "Acracanthus atokaensis" for the genus and species in his unpublished 1947 master's thesis, but the name was changed to Acrocanthosaurus atokensis for formal publication.

The holotype and paratype (OMNH 10146 and OMNH 10147), discovered in the early 1940s and described at the same time in 1950, consist of two partial skeletons and a piece of skull material from the Antlers Formation in Oklahoma. Two much more complete specimens were described in the 1990s. The first (SMU 74646) is a partial skeleton, missing most of the skull, recovered from the Twin Mountains Formation of Texas and currently part of the Fort Worth Museum of Science and History collection. An even more complete skeleton (NCSM 14345, nicknamed "Fran") was recovered from the Antlers Formation of Oklahoma by Cephis Hall and Sid Love, prepared by the Black Hills Institute in South Dakota, and is now housed at the North Carolina Museum of Natural Sciences in Raleigh. The specimen is the largest and includes the only known complete skull and forelimb. The skeletal elements of OMNH 10147 are almost the same size as comparable bones in NCSM 14345, indicating an animal roughly the same size, while the holotype and SMU 74646 are significantly smaller.

The presence of Acrocanthosaurus in the Cloverly Formation was established in 2012 with the description of another partial skeleton (UM 20796). The specimen, consisting of parts of two vertebrae, partial pubic bones, a femur, a partial fibula, and fragments, represents a juvenile animal. It came from a bonebed in the Bighorn Basin of north-central Wyoming and was found near the shoulder blade of a Sauroposeidon. An assortment of other fragmentary theropod remains from the formation may also belong to Acrocanthosaurus, which may be the only large theropod in the Cloverly Formation.

Unlike many other dinosaur genera, much less large theropods, Acrocanthosaurus inhabited both the western and eastern regions of the North American continent. The presence of the genus in the Arundel Formation of Maryland (roughly concurrent with the western formations) had long been suspected, with teeth almost identical to Acrocanthosaurus previously known from the formation. In 2024, an incomplete theropod skeleton (USNM 466054) from the Arundel Formation was identified as that of a subadult Acrocanthosaurus, referred to as A. cf. atokensis, marking the first definitive record of the genus from eastern North America. This skeleton, the most completely known theropod specimen from the formation despite its fragmentary nature, had been previously identified as an ornithomimosaur until this study and also represents the smallest known individual of the genus.

Acrocanthosaurus may be known from incomplete remains outside Oklahoma, Texas, Wyoming, and Maryland. A tooth from southern Arizona has been referred to the genus, and matching tooth marks have been found in sauropod bones from the same area. Many other teeth and bones from various geologic formations throughout the western United States have also been referred to as Acrocanthosaurus, but most of these have been misidentified; there is, however, some disagreement with this assessment regarding fossils from the Cloverly Formation.

Acrocanthosaurus was among the largest theropods known to exist, with an estimated skull length of 1.23–1.29 m (4.0–4.2 ft) and body length of 11.0–11.5 m (36.1–37.7 ft), based on the largest known specimen (NCSM 14345). Researchers have yielded body mass estimates for this specimen between 4.4 and 8.4 metric tons (4.9 and 9.3 short tons) based on various techniques.