2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/14475The processes contributing to the evolution of an initially weak magnetic field in a differentially rotating star are reviewed. These include rotational smoothing (akin to convective expulsion) and a list of about 5 instabilities, among them magnetorotational instability, byoyancy instability, and pinch-type instabilities. The important effects of thermal and magnetic diffusion on these instabilities are analyzed in some detail. The first instability to set in is a pinch-type instability. It becomes important in modifying the field configuration before magnetic buoyancy-driven instabilities set in. The evolution of an initially strong field remains a more open question, including the old problem whether dynamically stable magnetic equilibria exist in stars.Accepted for publication in A&AAstrophysicstext