Literature data for the solubility of anhydrous lithium hydroxide and lithium hydroxide monohydrate in pure water have been compiled and critically evaluated. The selected data have been represented by empirical temperature-molality expressions from which the coordinates of the eutectic and of the peritectic have been calculated. The phase diagram of the LiOH + H2O system is presented. A model using Pitzer's ion interaction approach for the calculation of the thermodynamic properties of aqueous LiOH solutions is built by fitting literature values for the osmotic coefficient obtained from isopiestic and from freezing point depression measurements from the eutectic point (255 K) to 473 K. Heat capacities of aqueous LiOH solutions are then calculated using the first and second derivatives with respect to temperature of these expressions and are compared to direct measurements. The solubility products of LiOH(s) and of LiOH center dot H2O(s) are calculated from their solubilities in pure water. Standard entropies, enthalpies, and heat capacities of formation of solid lithium hydroxides retrieved from fits of their solubility products with respect to temperature are compared to literature values, which are mainly derived from calorimetric measurements.