Stenonychosaurus (type genus S. inequalis) was named by C.M. Sternberg in 1932, based on a foot, wreckage of a hand, and some caudal vertebrae from the Late Cretaceous of Alberta. An extraordinary feature of these remains was the distended claw on the second toe, now recognized as trait of Deinonychosauria. Sternberg initially classified Stenonychosaurus as a associate of the family Coeluridae within the theropod dinosaurs. Later, Sternberg (1951) speculated that since Stenonychosaurus had a "very peculiar pes" and Troodon "equally strange teeth", they may be closely related. Unluckily, no comparable specimens were obtainable at that time to test the idea.
A more whole skeleton of Stenonychosaurus was described by D.A. Russell in 1969, which eventually shaped the scientific foundation for a famous life-sized sculpture of Stenonychosaurus accompany by its fictional, human-like descendant, the "dinosauroid". Stenonychosaurus became a well-known theropod in the 1980s, when the feet and braincase were described in more elements. It is sometimes listed as the "most intelligent" of dinosaurs. P.J. Currie reviewing the known Troodontidae in 1987, reclassified Stenonychosaurus inequalis as a junior synonym of Troodon formosus. This synonomy has been extensively adopted by other paleontologists, and therefore all of the specimens once called Stenonychosaurus are now referred to as Troodon in the recent scientific text. Other taxa "lumped" into Troodon are Pectinodon bakkeri and Polyodontosaurus grandis, which, the length of with Stenonychosaurus inequalis may all be separate suitable species, or belonging to one genus or species.