  The early stages of the pre-Main-Sequence (PMS) evolution of young stars are
characterized by a substantial interaction between the central star and the
surrounding disk. Among the processes that take place, the accretion of
material from the disk onto the star is a crucial one, as it traces the disk
evolution and, in turn, affects how planets are formed and evolve in disks.
Even if accretion has been studied for many years, it is still the focus of a
large body of work, as we do not fully understand how it happens.
