Megalosauridae is a monophyletic family of carnivorous theropod dinosaurs. It comes from the order Saurischia and the clade Tetanurae, and is closely related to the families Allosauridae and Spinosauridae. Some members of this family include Megalosaurus, Torvosaurus, Eustreptospondylus, and Streptospondylus. Appearing in the Middle Jurassic, megalosaurids are a relatively primitive group characterized by two unambiguous synapomorphies: a humeral deltopectoral crest that terminates about halfway along the humeral shaft and the absence of a fibular anterolateral tubercle. Megalosauridae contains two main subfamilies- Megalosaurinae, defined as all megalosaurids closer to Megalosaurus than Afrovenator, and Afrovenatorinae, defined as megalosaurids closer to Afrovenator than Megalosaurus.

The defining megalosaurid is Megalosaurus bucklandii, first named and described in 1824 by William Buckland after multiple finds in Stonesfield, Oxfordshire, UK. Megalosaurus was the first formally described dinosaur and was the basis for the establishment of the clade Dinosauria. It is also one of the largest known Middle Jurassic carnivorous dinosaurs, with the best-preserved femur at 805 mm and a proposed body mass of around 943 kg. Megalosauridae is recognized as a mainly European group of dinosaurs, based on fossils found in France and the UK. However, recent discoveries in Niger have led some to consider the range of the family. Megalosaurids appeared right before the split of the supercontinent Pangaea into Gondwana and Laurasia.These large theropods therefore may have dominated both halves of the world during the Jurassic.

The family Megalosauridae was first defined by Thomas Huxley in 1869, yet it has been contested throughout history due to its role as a ‘waste-basket’ for many partially described dinosaurs or unidentified remains. In the early years of paleontology, most large theropods were grouped together and up to 48 species were included in the clade Megalosauria, the basal clade of Megalosauridae. Over time, most of these taxa were placed in other clades and the parameters of Megalosauridae were narrowed significantly. However, some controversy remains over whether Megalosauridae should be considered its own distinct group, and dinosaurs in this family remain some of the most problematic taxa in all Dinosauria. Some paleontologists, such as Paul Sereno in 2005, have disregarded the group due to its shaky foundation and lack of clarified phylogeny. However, recent research by Carrano, Benson, and Sampson has systematically analyzed all basal tetanurans and determined that Megalosauridae should exist as its own family.

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