Stephen Polyak (born Stjepan Lucian Poljak; December 13, 1889 – March 9, 1955) was an American neuroanatomist and neurologist considered to be one of the most prominent neuroanatomists of the 20th century.

Polyak studied the functional structure of the organs of sight and hearing, explaining the function of the retina and the cochlea, and visual and auditory pathways and centers. He also gave a new interpretation of the basic visual processes.