兽脚亚目（拉丁名：Theropoda）属于蜥臀目，是群双足恐龙。虽然牠们主要是肉食性动物，但是在白垩纪时期，一部份的兽脚类恐龙演变成为草食性、杂食性、甚至食虫动物。兽脚类最早出现在三叠纪晚期的卡尼阶，大约是2亿3000万年前。牠们从侏㑩纪早期开始成为独占广大陆地的肉食动物，直到6500万年前的白垩纪结束为止。

兽脚亚目后来演变出一类特殊的小型恐龙，称为虚骨龙类（Coelurosauria），可能是拥有9,300个物种的鸟类的共同祖先，鸟类在侏㑩纪晚期出现。兽脚亚目与鸟类之间的共同点包括：脚掌有三趾（牠们的第一趾其实萎缩在脚部后方）、胸部上的「叉骨」、与充满空气的骨头。此外，某些兽脚类恐龙拥有羽毛和孵卵行为。

Theropoda (/θɪərˈɒpədə/ or /ˌθɪərəˈpoʊdə/, from Greek θηρίον "wild beast" and πούς,πόδις "foot") or theropods (/ˈθɪərəˌpɒdz/) are a group of saurischian dinosaurs. Theropods were ancestrally carnivorous, although a number of theropod groups evolved herbivory, omnivory, piscivory, and insectivory. Theropods first appeared during the Carnian age of the late Triassic period 231.4 million years ago (Ma) and included the sole large terrestrial carnivores from the Early Jurassic until at least the close of the Cretaceous, about 66 Ma. In the Jurassic, birds evolved from small specialized coelurosaurian theropods, and are today represented by 10,000 living species.