Compiled by David Chalmers
Zombies are hypothetical creatures of the sort that philosophers have been known to cherish. A zombie is physically identical to a normal human being, but completely lacks conscious experience. (Here is a brief case-study.) Zombies look and behave like the conscious beings that we know and love, but "all is dark inside." There is nothing it is like to be a zombie.
(Note that these zombies need to be distinguished from Hollywood zombies and Haitian voodoo zombies, which typically have behavioral impairments and may have some sensory experiences. They are also not to be confused with the drink, the Unix process, or the 1960s pop group.)
Very few people think that zombies could exist in the actual world (i.e., that they are naturally or nomologically possible), but many people think that they are at least logically possible - i.e. that the idea of zombie is internally consistent, and that there is at least a "possible world" where zombies exist. This logical possibility is sometimes used to draw strong conclusions about consciousness (e.g. in my book The Conscious Mind, and elsewhere).
The general point is that the logical possibility of zombies is one way of illustrating that there is no logical entailment from physical facts to facts about consciousness, whereas there is such an enatilment in most other domains. Of course even the logical possibility of zombies is controversial to some (e.g. Dennett ), as conceivability intuitions are notoriously elusive; and some scientists have been known to wonder whether anything important really follows from what is merely conceivable. I think that most arguments that use zombies can actually be rephrased in a zombie-free way, so that these arguments can be set aside if one prefers; but zombies at least provide a vivid and provocative illustration.
(A related idea is that of a functional isomorph of a normal human that lacks conscious experience: perhaps a system with silicon chips instead of neurons, for example. This has occasionally been called a "functional zombie", though usually it goes by the more prosaic name of "absent qualia". Some use the logical possibility of such a functional zombie to argue against reductive functionalist theories of consciousness. Of these, some go further and argue that functional zombies might even exist in the actual world, suggesting that any form of functionalism or AI is doomed. Others (like me) deny this, so that the mere logical possibility of zombies doesn't stand in the way of AI.)
As far as I know, the first paper in the philosophical literature to talk explicitly and at length about zombies was Robert Kirk's "Zombies vs. Materialists" in Mind in 1974, although Keith Campbell's 1970 book Body and Mind talks about an "imitation-man" which is much the same thing. After that, there was hardly any explicit discussion of zombies in the philosophical literature for a long time (although there was quite a lot on "absent qualia", i.e. functional zombies). When I wrote my 1993 Ph.D. thesis. in which zombies played a central role, there was hardly anything out there. But for one reason or another, zombies have risen from the grave in the last couple of years; and they turn out to be unaccountably well-represented on the web, in particular.
So here are a few links for the zombieholic.
Papers on zombies
Other philosophical zombie resources
Zombies of all varieties
Thanks especially to Larry Hauser and his zombie page for giving me the idea.