In the idealized theory of toroidal magnetic confinement, the plasma is supposed to be embedded in a nested set of topologically toroidal magnetic surfaces. The plasma is assumed to be stable so that all transport processes, such as thermal conduction, are determined only by Coulomb collisions between the particles. In this paper, we first compare the experimental results with the predictions of this theory. The actual energy transport rate is found to be much higher than that predicted. This is believed to be due to instability processes in the plasma although there remains the possibility that the idealized or classical theory is not complete. The role of electrostatic and of magnetic instabilities is discussed. Finally, the consequences of a simple model, in which the form of the temperature profile is fixed, are discussed.