Dick, Philip K. Do Androids Dream of ELectric Sheep. ISBN 0345350472 216 pgs.
An interesting take on the question
What is a person? Dick lost me in a couple of places, but it may have been the drugs taken while writing. In spite of that I was on my toes the entire story! Deckard is a bounty hunter who is supposed to track down androids who have escaped
lives of servitude in off-world colonies and secreted themselves on earth. The difference between andies and humans is that andies have a less developed sense of morals than humans, even toward other androids. (Apparently they die after a few years too.) Deckard begins to question this somewhat. In the end the question is not answered.
(One nagging questoin in the back of my mind still is: why do androids need to be retured anyway?)