  Polarization has opened a new physics chapter in relativistic heavy-ion
collisions. Since the first prediction and experimental observation of global
spin polarization, a lot of progress has been made in understanding its
features, both at experimental and theoretical level. In this paper, we give an
overview on the recent advances in this field. The covered topics include a
review of measurements of global and local spin polarization of hyperons and
the global spin alignment of vector mesons. We account for the basic
theoretical framework to describe spin polarization in a relativistic fluid
such as the Quark Gluon Plasma, including statistical quantum field theory and
local thermodynamic equilibrium, spin hydrodynamics, relativistic kinetic
theory with spin and coalescence models.
