Do all animals have rights? Is it morally wrong to use mice or dogs in medical research, or rabbits and cows as food? How ought we resolve conflicts between the interests of humans and those of other animals? Philosophical inquiry is essential in addressing such questions; the answers given have enormous practical importance. Here for the first time in the same volume, the animal rights debate is argued deeply and fully by the two most articulate and influential philosophers representing the opposing camps, and an enduring controversy receives its deepest and most eloquent exposition.