Lithium nitrate trihydrate is of interest as a thermal energy storage material, due to its large specific and volumetric enthalpy of fusion and its low melting temperature. Here, we report the thermophysical properties of solid and liquid lithium nitrate trihydrate at temperatures from (253 to 353) K and compare this compound to water and octadecane, two other potential thermal energy storage materials. Furthermore, we examine the lithium nitrate-water phase diagram and accurately determine the enthalpies of fusion and melting temperatures for lithium nitrate trihydrate, Delta H-fus, = (287 +/- 7) J.g(-1) and T-fus = 303.3 K, and the lithium nitrate trihydrate-lithium nitrate eutectic, Delta H-fus = (264 +/- 2) J.g(-1) and T-fus = 301.4 K.