This joint session invites contributions from Solar Physics and Astronomy on the structure and dynamics of magnetic fields. The magnetic field of a star facilitates the transport of energy from the interior to the atmosphere and beyond, and is therefore essential for understanding the appearance of stars in general and our Sun in particular. The focus of this session will be to address the nature of generic structures of magnetic fields. This includes dynamo action, energy transport and release mechanisms, as well as observational consequences such as heating and acceleration of particles or flows due to the relaxation of magnetic fields.