Stellar structure and magnetic fields from pre-main sequence to cataclysmic binaries

I review the problem of lithium depletion in pre-Main Sequence (pre-MS) stars, and the curious points of view which accompanied the changes in the results due to the changes in the stellar physics inputs in the last 35 years. Today, the problem of explaining the present solar lithium abundance is reversed with respect to the problem of some years ago: new standard stellar models deplete too much lithium during the pre-MS evolution. We have recently attempted to model the solar pre-MS by including the thermal effect of the magnetic field which is due to the rotationally induced dynamo in these stars. I show that this new physical input can not only help to correctly describe the pre-MS lithium depletion, but it can also provide the correct HR diagram location for the first eclipsing pre-MS binary having a component of mass close to solar, RXJ 0529.4+0041. We show that the same model can be applied to the fast rotating secondaries of cataclysmic binaries and help to solve the problem of matching the observed minimum orbital period with the theoretical period.