We review some of the theoretical interpretations which have been given for the formation of the high E→r x B→ rotation shear layer observed concomitantly with the transition to and the operation in the high confinement mode. Those can be classified as follows: the origin of the large radial electric field is (i) anomalous, (ii) associated with loss of ions along open orbits (i.e. crossing the separatrix), (iii) related to the decoupling of the ion and electron flows by finite Larmor radius effects and inertia. It is generally accepted that E→r x B→ shear reduces the level of microturbulence and thus of anomalous transport; this point of view is adopted here and explained.