Ornithopsis was named by Seeley (1870). It is the type genus of Ornithopsidae.

It was replaced with Bothriospondylus by Owen (1875); it was synonymized subjectively with Chondrosteosaurus by Sauvage (1880); it was synonymized subjectively with Cetiosaurus by Dollo (1889); it was synonymized subjectively with Pelorosaurus by Lydekker (1889), Huene (1908), Huene (1909), Huene (1927), Huene (1927), Romer (1956), Tatarinov (1964), Romer (1966), Steel (1970), McIntosh (1990); it was synonymized subjectively with Hoplosaurus by Lydekker (1893), Lydekker (1895); it was synonymized subjectively with Eucamerotus by Apesteguía (2005); it was considered a nomen dubium by Naish and Martill (2001).

It was assigned to Ornithopsidae by Lydekker (1887); to Dinosauria by Mansel-Pleydell (1888); to Cetiosauridae by Depéret (1896); to Sauropoda by Sauvage (1882), Marsh (1884), Marsh (1885), Marsh (1895), Gadow (1897); to Sauropoda by Gadow (1898), Gadow (1901); to Atlantosauridae by Hulke (1887), Lydekker (1888), Nopcsa (1901), Mansel-Pleydell (1902); to Cardiodontidae by Marsh (1896), Marsh (1898), Sauvage (1900), Sauvage (1906); to Sauropoda by Seeley (1879), Joleaud (1922); to Morosauridae by Dollo (1884), Zittel (1890), von Zittel (1911), Lull (1924); to Camarasaurinae by Nopcsa (1928); to Brachiosaurinae by Swinton (1970); to Camarasauridae by Martill (1988); to Brachiosauridae by Swinton (1936), Delair (1960), Blows (1995), Norman (1997), Blows (1998), Naish and Martill (2007); and to Titanosauriformes by Upchurch et al. (2004), Mannion (2010), Mannion and Calvo (2011).