Spin polarization in relativistic heavy-ion collisions has emerged as a significant area of research, offering new insights into the properties of quantum chromodynamics (QCD) matter. This paper reviews recent advances in understanding spin polarization, focusing on both experimental and theoretical aspects. The study covers the measurement of global and local spin polarization of hyperons and the global spin alignment of vector mesons. Theoretical frameworks include quantum statistical field theory, local thermodynamic equilibrium, spin hydrodynamics, and relativistic kinetic theory with spin and coalescence models. The concept of global spin polarization was first proposed in 2004, suggesting that particles produced in heavy-ion collisions at finite impact parameter could be globally polarized along the direction of the total orbital angular momentum. Theoretical predictions based on spin-orbit coupling in a QCD-inspired model suggested large polarization values, though later corrected to be less than 4%. The idea of polarization related to hydrodynamic motion, particularly vorticity, was proposed around the time of the first measurement of global Λ polarization at RHIC, leading to quantitative predictions based on hydrodynamic vorticity. These predictions, released around 2015, suggested a global polarization of about 1% for Λ hyperons at 200 GeV, consistent with experimental data. Experiments such as STAR have confirmed these findings, showing positive evidence of global spin polarization of Λ hyperons in Au+Au collisions. The results align with hydrodynamic and local equilibrium models, confirming the link between spin and rotation, a concept observed in the Barnett and Einstein-De Haas effects. Spin polarization has been observed at various energies, including very low and high energies, and is not solely due to hadron-dependent couplings but rather collective system properties. Local spin polarization, as a function of the azimuthal angle of emission, has shown discrepancies with predictions from hydrodynamic models and local equilibrium. This has motivated theoretical studies, leading to advancements in spin thermodynamics and kinetics. The development of kinetic theory with spin and relativistic hydrodynamics with a quantum spin tensor has been crucial. Recent calculations within the local equilibrium framework have revealed contributions from the thermal shear tensor, which, when combined with thermal vorticity, helps explain experimental data. The spin density matrix and spin alignment of vector mesons have been studied, with spin alignment defined as the difference between the spin density matrix element and its value in the absence of polarization. Measurements of spin alignment for vector mesons like the φ and K*0 have shown small but measurable deviations from 1/3, consistent with theoretical predictions involving quark recombination and vector fields. This review highlights the ongoing development of spin physics in relativistic heavy-ion collisions, emphasizing its potential to probe fundamental aspects of QCD matter, including local parity violation, energy loss of partons, and the critical point in the QCD phase diagram. The field is rapidly evolving, and future research will continue to explore these phenomenaSpin polarization in relativistic heavy-ion collisions has emerged as a significant area of research, offering new insights into the properties of quantum chromodynamics (QCD) matter. This paper reviews recent advances in understanding spin polarization, focusing on both experimental and theoretical aspects. The study covers the measurement of global and local spin polarization of hyperons and the global spin alignment of vector mesons. Theoretical frameworks include quantum statistical field theory, local thermodynamic equilibrium, spin hydrodynamics, and relativistic kinetic theory with spin and coalescence models. The concept of global spin polarization was first proposed in 2004, suggesting that particles produced in heavy-ion collisions at finite impact parameter could be globally polarized along the direction of the total orbital angular momentum. Theoretical predictions based on spin-orbit coupling in a QCD-inspired model suggested large polarization values, though later corrected to be less than 4%. The idea of polarization related to hydrodynamic motion, particularly vorticity, was proposed around the time of the first measurement of global Λ polarization at RHIC, leading to quantitative predictions based on hydrodynamic vorticity. These predictions, released around 2015, suggested a global polarization of about 1% for Λ hyperons at 200 GeV, consistent with experimental data. Experiments such as STAR have confirmed these findings, showing positive evidence of global spin polarization of Λ hyperons in Au+Au collisions. The results align with hydrodynamic and local equilibrium models, confirming the link between spin and rotation, a concept observed in the Barnett and Einstein-De Haas effects. Spin polarization has been observed at various energies, including very low and high energies, and is not solely due to hadron-dependent couplings but rather collective system properties. Local spin polarization, as a function of the azimuthal angle of emission, has shown discrepancies with predictions from hydrodynamic models and local equilibrium. This has motivated theoretical studies, leading to advancements in spin thermodynamics and kinetics. The development of kinetic theory with spin and relativistic hydrodynamics with a quantum spin tensor has been crucial. Recent calculations within the local equilibrium framework have revealed contributions from the thermal shear tensor, which, when combined with thermal vorticity, helps explain experimental data. The spin density matrix and spin alignment of vector mesons have been studied, with spin alignment defined as the difference between the spin density matrix element and its value in the absence of polarization. Measurements of spin alignment for vector mesons like the φ and K*0 have shown small but measurable deviations from 1/3, consistent with theoretical predictions involving quark recombination and vector fields. This review highlights the ongoing development of spin physics in relativistic heavy-ion collisions, emphasizing its potential to probe fundamental aspects of QCD matter, including local parity violation, energy loss of partons, and the critical point in the QCD phase diagram. The field is rapidly evolving, and future research will continue to explore these phenomena