  New solar models are presented, which have been computed with the most recent
physical inputs (nuclear reaction rates, equation of state, opacities,
microscopic diffusion). Rotation-induced mixing has been introduced in a way
which includes the feed-back effect of the $\mu$-gradient induced by helium
settling. A parametrization of the tachocline region below the convective zone
has also been added in the computations. The sound velocities have been
computed in the models and compared to the seismic sun. Our best model is
described in some detail. Besides the new physical inputs, the most important
improvement concerns the computations of $\mu$-gradients during the solar
evolution and their influence in slowing down rotation-induced mixing. This
process can explain why lithium is depleted in the present Sun while beryllium
is not, and meanwhile why $^3$He has not increased at the solar surface for at
least 3 Gyrs.
