Where does the mind stop and the rest of the world begin? Some philosophers are now arguing that thoughts are not all in the head. The environment has an active role in driving cognition; cognition is sometimes made up of neural, bodily, and environmental processes. Their argument has excited a vigorous debate among philosophers and this week we discover what the fuss is about. We hear from two proponents of the extended mind thesis from one of its critics, Robert Rupert, associate professor of philosophy at the University of Colorado, Boulder.