偷蛋龙下目（Oviraptorosauria）是群兽脚亚目手盗龙类恐龙，生存于白垩纪的亚洲与北美洲。牠们拥有喙状嘴、羽毛，头顶具有骨质冠饰。偷蛋龙下目包含偷蛋龙科、近颌龙科、以及数个不属于以上科的物种，包括拟鸟龙、尾羽龙、以及原始祖鸟。牠们的体型从小如火鸡的尾羽龙，大至8公尺长、1.4公吨重的巨盗龙。如同其他手盗龙类，偷蛋龙下目接近鸟类的祖先，牠们曾经被认为事实上代表者原始的无法飞行鸟类。目前最完整的偷蛋龙类化石，发现于亚洲；而北美洲的偷蛋龙类化石，则零缺较不完整。

目前已知最古老的偷蛋龙类是原始祖鸟、切齿龙，也是体型最粗壮的偷蛋龙类。原始祖鸟、切齿龙的化石都发现于中国辽宁省的义县组，地质年代约1亿2500万年前，相当于白垩纪早期的阿普第阶。簧椎龙、鞘虚骨龙的化石状态破碎，有可能是偷蛋龙类的原始物种。近年在英格兰的瓦德赫斯特粘土组（Wadhurst Clay Formation）地层发现的ㄧ节小型脊椎骨，拥有类似偷蛋龙类的特征，而这地层的年代约1亿4000万年前。如果这化石属于偷蛋龙类，将使偷蛋龙类的演化起源食代提早。

Oviraptorosaurs ("egg thief lizards") are a group of feathered maniraptoran dinosaurs from the Cretaceous Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot-like skulls, with or without bony crests atop the head. They ranged in size from Caudipteryx, which was the size of a turkey, to the 8 metre long, 1.4 ton Gigantoraptor. The group (along with all maniraptoran dinosaurs) is close to the ancestry of birds. Analyses like those of Maryanska et al (2002) and Osmólska et al. (2004) suggest that they may represent primitive flightless birds. The most complete oviraptorosaur specimens have been found in Asia. The North American oviraptorosaur record is sparse.