The paper provides an overview of recent advances in the field of spin polarization in relativistic heavy-ion collisions. It covers both experimental and theoretical aspects, including measurements of global and local spin polarization of hyperons and the global spin alignment of vector mesons. The theoretical framework discussed includes quantum statistical field theory, local thermodynamic equilibrium, spin hydrodynamics, and relativistic kinetic theory with spin. The paper highlights the development of understanding spin polarization in relativistic fluids, particularly in the context of Quark Gluon Plasma (QGP), and addresses discrepancies between theoretical predictions and experimental findings. It also discusses the role of spin polarization in probing the properties of QGP and its potential applications in physics.The paper provides an overview of recent advances in the field of spin polarization in relativistic heavy-ion collisions. It covers both experimental and theoretical aspects, including measurements of global and local spin polarization of hyperons and the global spin alignment of vector mesons. The theoretical framework discussed includes quantum statistical field theory, local thermodynamic equilibrium, spin hydrodynamics, and relativistic kinetic theory with spin. The paper highlights the development of understanding spin polarization in relativistic fluids, particularly in the context of Quark Gluon Plasma (QGP), and addresses discrepancies between theoretical predictions and experimental findings. It also discusses the role of spin polarization in probing the properties of QGP and its potential applications in physics.