The stellar magnetic dynamo during the evolution across the main sequence

In comparison with stellar magnetic field studies in the eighties and nineties, where most effort was focused on A, B, and active solar-type stars, magnetic fields are currently directly measured in massive early B and O stars with radiative envelopes, as well as in the lower mass tail consisting of fully convective late-M dwarfs. Knowledge of the magnetic field topology of stars of different mass and at different evolutionary stages is important to understand the underlying magnetic field generation mechanisms. I review the present status of magnetic field studies along with the results of theoretical modeling.