John Cunningham Lilly (January 6, 1915 - September 30, 2001) was an American physician, psychoanalyst and writer.

He was a pioneer researcher into the nature of consciousness using as his principal tools the isolation tank, dolphin communication and psychedelic drugs, sometimes in combination. He was a prominent member of the Californian counterculture of scientists, mystics and thinkers that arose in the late 1960s and early 70s. Albert Hofmann, Gregory Bateson, Ram Dass, Timothy Leary, Werner Erhard, and Richard Feynman were all frequent visitors to his home.