This review discusses the theoretical background, experimental techniques, and phenomenology of the Glauber Model in relativistic heavy ion physics. The Glauber Model is used to calculate geometric quantities such as impact parameter (b), number of participating nucleons (N_part), and number of binary nucleon-nucleon collisions (N_coll). The model has evolved from its original form into a purely classical geometric approach used for modern data analysis. It distinguishes between the "optical limit" and Monte Carlo approaches, which are often used interchangeably but have essential differences in specific contexts. The methods used by the four RHIC experiments are compared, with similar results for geometric observables. Several important RHIC measurements are highlighted that rely on geometric quantities estimated from Glauber calculations to draw insights from experimental data. The status and future of Glauber modeling in the next generation of heavy ion physics studies are briefly discussed. The Glauber Model is based on the interaction of nucleons in nuclear targets, with the optical limit used to make the full multiple scattering integral numerically tractable. The Monte Carlo approach is used to simulate experimental data and estimate geometric quantities. The model is applied to various collision systems, including p+A and A+A collisions, and is used to study the geometry of collisions, including eccentricity and elliptic flow. The model is also used to study the absorption of J/ψ particles in nuclear matter. The review discusses the differences between the optical and Monte Carlo approaches, and the importance of geometric quantities in understanding heavy ion collisions. The Glauber Model is used to estimate the number of participants and collisions in heavy ion collisions, and is applied to various experimental data. The review highlights the importance of geometric quantities in understanding the dynamics of nucleus-nucleus collisions and the future of Glauber modeling in heavy ion physics.This review discusses the theoretical background, experimental techniques, and phenomenology of the Glauber Model in relativistic heavy ion physics. The Glauber Model is used to calculate geometric quantities such as impact parameter (b), number of participating nucleons (N_part), and number of binary nucleon-nucleon collisions (N_coll). The model has evolved from its original form into a purely classical geometric approach used for modern data analysis. It distinguishes between the "optical limit" and Monte Carlo approaches, which are often used interchangeably but have essential differences in specific contexts. The methods used by the four RHIC experiments are compared, with similar results for geometric observables. Several important RHIC measurements are highlighted that rely on geometric quantities estimated from Glauber calculations to draw insights from experimental data. The status and future of Glauber modeling in the next generation of heavy ion physics studies are briefly discussed. The Glauber Model is based on the interaction of nucleons in nuclear targets, with the optical limit used to make the full multiple scattering integral numerically tractable. The Monte Carlo approach is used to simulate experimental data and estimate geometric quantities. The model is applied to various collision systems, including p+A and A+A collisions, and is used to study the geometry of collisions, including eccentricity and elliptic flow. The model is also used to study the absorption of J/ψ particles in nuclear matter. The review discusses the differences between the optical and Monte Carlo approaches, and the importance of geometric quantities in understanding heavy ion collisions. The Glauber Model is used to estimate the number of participants and collisions in heavy ion collisions, and is applied to various experimental data. The review highlights the importance of geometric quantities in understanding the dynamics of nucleus-nucleus collisions and the future of Glauber modeling in heavy ion physics.