Impressive events of magnetic energy release, such as solar and stellar flares and coronal mass ejections, take place in the atmospheric layers above a star's photosphere. These magnetic-activity events are closely related to the dynamics of subsurface convection zones inside the star. IAU Symposium 365 was devoted to observational and theoretical aspects of solar and stellar hydrodynamics and magnetohydrodynamics, both global and local, including numerical studies. The last few decades have been marked by substantial progress in our understanding of the physics of internal and external processes in the Sun and solar-type stars, but the scientific communities making this progress have not traditionally worked closely together. This symposium, delayed due to the COVID pandemic, brought together specialists in the physics of convection zones and atmospheres, to stimulate the emergence of new ideas and to develop new techniques in this dynamic field of active research.