Experiments have been performed to measure the effect of additives on the crystallization temperature of concentrated LiBr solutions cooled at a rate of 20 • C/h. The measured crystallization temperatures correspond not to the temperatures of equilibrium solubility but to the critical temperature for heterogeneous nucleation of the hydrated LiBr salt on the glass wall of the test tube containing the sample solution. Various additives at concentrations from 250 to 1500 ppm have been investigated. Some soluble additives further decreased the experimental crystallization temperature by as much as 13 • C, corresponding to 22 • C below the equilibrium solubility. Large decreases in the crystallization temperature can be correlated with large values of complexation constants of the additive for either the Li + or the Br -ion in solution. Solution complexation, however, is not sufficient to explain the magnitude of the decrease in the crystallization temperature. The only phenomenon capable of quantitatively explaining the magnitude of the decrease in the crystallization temperature is the change in the crystal/solution interfacial energy due to adsorption of the additive on the surface of the prenucleation embryos. A quantitative model of the crystal/solution interfacial energy due to adsorption has been developed using both the Langmuir and Gibbs adsorption equations, allowing the quantitative prediction of crystallization temperatures with additive concentration.