New forms of QCD matter, specifically the Quark-Gluon Plasma (QGP) and Color Glass Condensate (CGC), have been discovered at the Relativistic Heavy Ion Collider (RHIC). The QGP is a state of matter where quarks and gluons are deconfined and in thermal equilibrium, while the CGC represents a high-energy, strongly interacting initial state of matter. Empirical evidence from RHIC experiments, including data from p + p, D + Au, and Au + Au collisions at energies up to 200 AGeV, supports the existence of these states. The QGP is produced through high-energy collisions, and its source is linked to a saturated gluon CGC initial state. The CGC is characterized by a universal initial density matrix and is relevant for high-energy interactions, including those in heavy-ion collisions. The QGP is a strongly coupled state of matter at high temperatures, while the CGC is a coherent state at high energies. Both forms of matter are essential for understanding the behavior of QCD under extreme conditions. The QGP is expected to form when the energy density of matter reaches that of a proton, and its properties are studied through collective flow patterns and other observables. The CGC is important for understanding the initial conditions of high-energy collisions and provides a framework for predicting the evolution of matter in these collisions. Empirical evidence from RHIC experiments, such as elliptic flow measurements, supports the existence of a QGP with properties consistent with thermal equilibrium. The observed collective flow patterns, particularly the elliptic flow, are consistent with hydrodynamic predictions and indicate that the QGP is in local thermal equilibrium. The CGC is also supported by data showing that the initial state of collisions can be described by a saturated gluon distribution. These findings highlight the importance of RHIC in exploring the properties of QCD matter and provide a foundation for future studies of these new forms of matter.New forms of QCD matter, specifically the Quark-Gluon Plasma (QGP) and Color Glass Condensate (CGC), have been discovered at the Relativistic Heavy Ion Collider (RHIC). The QGP is a state of matter where quarks and gluons are deconfined and in thermal equilibrium, while the CGC represents a high-energy, strongly interacting initial state of matter. Empirical evidence from RHIC experiments, including data from p + p, D + Au, and Au + Au collisions at energies up to 200 AGeV, supports the existence of these states. The QGP is produced through high-energy collisions, and its source is linked to a saturated gluon CGC initial state. The CGC is characterized by a universal initial density matrix and is relevant for high-energy interactions, including those in heavy-ion collisions. The QGP is a strongly coupled state of matter at high temperatures, while the CGC is a coherent state at high energies. Both forms of matter are essential for understanding the behavior of QCD under extreme conditions. The QGP is expected to form when the energy density of matter reaches that of a proton, and its properties are studied through collective flow patterns and other observables. The CGC is important for understanding the initial conditions of high-energy collisions and provides a framework for predicting the evolution of matter in these collisions. Empirical evidence from RHIC experiments, such as elliptic flow measurements, supports the existence of a QGP with properties consistent with thermal equilibrium. The observed collective flow patterns, particularly the elliptic flow, are consistent with hydrodynamic predictions and indicate that the QGP is in local thermal equilibrium. The CGC is also supported by data showing that the initial state of collisions can be described by a saturated gluon distribution. These findings highlight the importance of RHIC in exploring the properties of QCD matter and provide a foundation for future studies of these new forms of matter.