 Many think that if the physical facts entail consciousness by metaphysical necessity, then physicalists can maintain that even though zombies are metaphysically impossible, they are still conceivable (Balog 2012; Loar 1990/97; McLaughlin 2005; Sections 5.1, 5.2 below). To the contrary, Chalmers argues that conceivability actually entails metaphysical possibility. If he is right, then that popular brand of physicalism is mistaken. The so-called ‘conceivability argument’ for the possibility of zombies will provide a focus for discussing some of the main problems raised by the zombie idea.