A comprehensive critical assessment has been made of the experimental data of the Mg-H system. Based on the selected original experimental phase diagram data from the literature, a set of thermodynamic functions for the Mg-H system was chosen and the parameters were optimized using the least squares method. Four different analytical descriptions were used to model the four different types of stable phases in the Mg-H system: gas, liquid, solid solution phase alpha-(Mg), and the stoichiometric compound beta-MgH2. Most of the experimental information is in agreement with the modeling, especially the dissociation pressures of MgH2 at different temperatures, the invariant equilibria, and the hydrogen solubilities in magnesium at one atmosphere. Calculation of the system has been used to thermodynamically analyze some experimental information.