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 Pelorosaurus by Lydekker (1889), Huene (1908), Huene (1909), Huene (1927), Huene (1927), Romer (1956), Romer (1966), Steel (1970) and McIntosh (1990); it was synonymized subjectively with Hoplosaurus by Lydekker (1893) and Lydekker (1895); it was synonymized subjectively with Eucamerotus by Apesteguía (2005).

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