A quasi-chemical reaction model has been developed to correlate vapor-liquid equilibrium data for the system ammonia (NH3) + water (H2O) + lithium bromide (LiBr) in the temperature range from 303.15 to 473.15 K and at pressures up to 2.0 MPa. This model assumes the formation of ion clusters, i.e., Lif and Br- ions surrounded by ammonia and water molecules. Further, ammonia and water molecules are assumed to form a second species of complexes. The activities of the various components in the liquid phase are modeled by the NRTL equation. The vapor phase, assumed to consist of ammonia and water only, is modeled by the equation of state of Ishikawa, Chung, and Lu.