Haldan Keffer Hartline (December 22, 1903 – March 17, 1983) was an American physiologist and biophysicist renowned for his pioneering research on the neural mechanisms of vision. He studied the transmission of signals in the visual system, particularly the interactions between photoreceptors and ganglion cells in the retina. In 1967, he shared the Nobel Prize in Physiology or Medicine with Ragnar Granit and George Wald for their discoveries concerning the primary physiological and chemical processes of vision. Hartline's work laid the foundation for modern neuroscience and ophthalmology.