The evolution of magnetic fields from the main-sequence to very late stages

Magnetic fields have been detected in most if not all types of stars across the Hertzsprung-Russell diagram. Where present, these fields have the potential to significantly impact the evolution of their host stars. Furthermore, they themselves are affected by the various structural changes which occur in a star during its life. For example, the significant radius expansion during the post-main-sequence phase, due to flux conservation, may lead to a decrease in surface magnetic field strength, to a point where the magnetic field may no longer be detectable. As a result, it is a challenge to link the magnetic fields observed in main sequence (MS) stars with those observed in very late stage stars and even to those in post-MS stars. In this review, I present what we know, from observations, about magnetic stars at various stages of stellar evolution.