Contrary to what is assumed in building standard stellar models, all stars undergo some mild mixing in their radiation zones. This mixing is due mainly to a slow thermally driven meridional circulation, and shear turbulence presumably contributes to it. It is the rotation of the star which is responsible for these motions, and therefore the transport of angular momentum must be described in time and space when modeling stellar evolution. This rotational mixing plays an important role in the evolution of massive stars; in particular it determines the late, pre-supernova phases. We review the present state of the problem and discuss briefly the open questions.